EP3064729A1 - Exhaust gas control system for internal combustion engine - Google Patents
Exhaust gas control system for internal combustion engine Download PDFInfo
- Publication number
- EP3064729A1 EP3064729A1 EP16158348.9A EP16158348A EP3064729A1 EP 3064729 A1 EP3064729 A1 EP 3064729A1 EP 16158348 A EP16158348 A EP 16158348A EP 3064729 A1 EP3064729 A1 EP 3064729A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- fuel ratio
- air
- internal combustion
- combustion engine
- catalyst
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
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- 238000002485 combustion reaction Methods 0.000 title claims abstract description 309
- 239000000446 fuel Substances 0.000 claims abstract description 447
- 239000003054 catalyst Substances 0.000 claims abstract description 406
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 claims description 243
- 229910021529 ammonia Inorganic materials 0.000 claims description 121
- 238000005086 pumping Methods 0.000 claims description 88
- 239000007789 gas Substances 0.000 claims description 86
- 238000010531 catalytic reduction reaction Methods 0.000 claims description 42
- 238000011144 upstream manufacturing Methods 0.000 claims description 41
- 238000000034 method Methods 0.000 claims description 38
- 230000007423 decrease Effects 0.000 claims description 31
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 30
- 229910052760 oxygen Inorganic materials 0.000 claims description 30
- 239000001301 oxygen Substances 0.000 claims description 30
- 231100000572 poisoning Toxicity 0.000 claims description 24
- 230000000607 poisoning effect Effects 0.000 claims description 24
- 229930195733 hydrocarbon Natural products 0.000 claims description 19
- 150000002430 hydrocarbons Chemical class 0.000 claims description 19
- 239000004215 Carbon black (E152) Substances 0.000 claims description 18
- 238000001514 detection method Methods 0.000 claims description 17
- 239000003638 chemical reducing agent Substances 0.000 claims description 12
- 238000000746 purification Methods 0.000 claims description 12
- 230000008859 change Effects 0.000 claims description 11
- 230000009467 reduction Effects 0.000 claims description 10
- 238000006722 reduction reaction Methods 0.000 claims description 10
- 230000008569 process Effects 0.000 description 30
- 239000002826 coolant Substances 0.000 description 19
- 230000004044 response Effects 0.000 description 9
- 238000002474 experimental method Methods 0.000 description 8
- 238000004088 simulation Methods 0.000 description 8
- 230000007812 deficiency Effects 0.000 description 7
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 6
- 230000008034 disappearance Effects 0.000 description 6
- 229910052717 sulfur Inorganic materials 0.000 description 6
- 239000011593 sulfur Substances 0.000 description 6
- 230000002950 deficient Effects 0.000 description 5
- 238000003795 desorption Methods 0.000 description 5
- 238000002347 injection Methods 0.000 description 5
- 239000007924 injection Substances 0.000 description 5
- 230000007246 mechanism Effects 0.000 description 4
- 238000006243 chemical reaction Methods 0.000 description 3
- 230000015556 catabolic process Effects 0.000 description 2
- 238000006731 degradation reaction Methods 0.000 description 2
- 230000003647 oxidation Effects 0.000 description 2
- 238000007254 oxidation reaction Methods 0.000 description 2
- 230000008030 elimination Effects 0.000 description 1
- 238000003379 elimination reaction Methods 0.000 description 1
- 239000010687 lubricating oil Substances 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 229910000069 nitrogen hydride Inorganic materials 0.000 description 1
- 238000001179 sorption measurement Methods 0.000 description 1
- 238000000629 steam reforming Methods 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
Images
Classifications
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02D—CONTROLLING COMBUSTION ENGINES
- F02D41/00—Electrical control of supply of combustible mixture or its constituents
- F02D41/02—Circuit arrangements for generating control signals
- F02D41/021—Introducing corrections for particular conditions exterior to the engine
- F02D41/0235—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus
- F02D41/0295—Control according to the amount of oxygen that is stored on the exhaust gas treating apparatus
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
- F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
- F01N3/0807—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents
- F01N3/0814—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents combined with catalytic converters, e.g. NOx absorption/storage reduction catalysts
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
- F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
- F01N3/0807—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents
- F01N3/0828—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents characterised by the absorbed or adsorbed substances
- F01N3/0842—Nitrogen oxides
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
- F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
- F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
- F01N3/103—Oxidation catalysts for HC and CO only
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
- F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
- F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
- F01N3/18—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
- F01N3/20—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion ; Methods of operation or control of catalytic converters
- F01N3/2066—Selective catalytic reduction [SCR]
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N9/00—Electrical control of exhaust gas treating apparatus
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02D—CONTROLLING COMBUSTION ENGINES
- F02D41/00—Electrical control of supply of combustible mixture or its constituents
- F02D41/02—Circuit arrangements for generating control signals
- F02D41/04—Introducing corrections for particular operating conditions
- F02D41/042—Introducing corrections for particular operating conditions for stopping the engine
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N2250/00—Combinations of different methods of purification
- F01N2250/12—Combinations of different methods of purification absorption or adsorption, and catalytic conversion
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N2430/00—Influencing exhaust purification, e.g. starting of catalytic reaction, filter regeneration, or the like, by controlling engine operating characteristics
- F01N2430/06—Influencing exhaust purification, e.g. starting of catalytic reaction, filter regeneration, or the like, by controlling engine operating characteristics by varying fuel-air ratio, e.g. by enriching fuel-air mixture
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N2560/00—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics
- F01N2560/02—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics the means being an exhaust gas sensor
- F01N2560/025—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics the means being an exhaust gas sensor for measuring or detecting O2, e.g. lambda sensors
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N2560/00—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics
- F01N2560/14—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics having more than one sensor of one kind
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N2610/00—Adding substances to exhaust gases
- F01N2610/02—Adding substances to exhaust gases the substance being ammonia or urea
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N2900/00—Details of electrical control or of the monitoring of the exhaust gas treating apparatus
- F01N2900/04—Methods of control or diagnosing
- F01N2900/0416—Methods of control or diagnosing using the state of a sensor, e.g. of an exhaust gas sensor
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N2900/00—Details of electrical control or of the monitoring of the exhaust gas treating apparatus
- F01N2900/06—Parameters used for exhaust control or diagnosing
- F01N2900/08—Parameters used for exhaust control or diagnosing said parameters being related to the engine
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N2900/00—Details of electrical control or of the monitoring of the exhaust gas treating apparatus
- F01N2900/06—Parameters used for exhaust control or diagnosing
- F01N2900/14—Parameters used for exhaust control or diagnosing said parameters being related to the exhaust gas
- F01N2900/1402—Exhaust gas composition
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N2900/00—Details of electrical control or of the monitoring of the exhaust gas treating apparatus
- F01N2900/06—Parameters used for exhaust control or diagnosing
- F01N2900/16—Parameters used for exhaust control or diagnosing said parameters being related to the exhaust apparatus, e.g. particulate filter or catalyst
- F01N2900/1602—Temperature of exhaust gas apparatus
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02D—CONTROLLING COMBUSTION ENGINES
- F02D2200/00—Input parameters for engine control
- F02D2200/02—Input parameters for engine control the parameters being related to the engine
- F02D2200/08—Exhaust gas treatment apparatus parameters
- F02D2200/0802—Temperature of the exhaust gas treatment apparatus
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02D—CONTROLLING COMBUSTION ENGINES
- F02D2200/00—Input parameters for engine control
- F02D2200/02—Input parameters for engine control the parameters being related to the engine
- F02D2200/08—Exhaust gas treatment apparatus parameters
- F02D2200/0802—Temperature of the exhaust gas treatment apparatus
- F02D2200/0804—Estimation of the temperature of the exhaust gas treatment apparatus
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02D—CONTROLLING COMBUSTION ENGINES
- F02D41/00—Electrical control of supply of combustible mixture or its constituents
- F02D41/02—Circuit arrangements for generating control signals
- F02D41/14—Introducing closed-loop corrections
- F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
- F02D41/1473—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the regulation method
- F02D41/1475—Regulating the air fuel ratio at a value other than stoichiometry
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T10/00—Road transport of goods or passengers
- Y02T10/10—Internal combustion engine [ICE] based vehicles
- Y02T10/12—Improving ICE efficiencies
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T10/00—Road transport of goods or passengers
- Y02T10/10—Internal combustion engine [ICE] based vehicles
- Y02T10/40—Engine management systems
Definitions
- the present disclosure relates to an exhaust gas control system for an internal combustion engine.
- NSR catalyst an NOx storage reduction catalyst
- the NSR catalyst stores NOx contained in exhaust gas when the concentration of oxygen in exhaust gas flowing into the NSR catalyst is high, and reduces the stored NOx when the concentration of oxygen in exhaust gas flowing into the NSR catalyst is low and there is a reducing agent.
- Sulfur poisoning of the NSR catalyst occurs because of a sulfur component that is contained in fuel.
- There is known a technique for, when there is a request to stop an internal combustion engine, actually stopping the internal combustion engine after sulfur poisoning of the NSR catalyst is eliminated see, for example, Japanese Patent Application Publication No. 10-231720 ( JP 10-231720 A )). With this technique, the internal combustion engine is caused to operate at a rich air-fuel ratio for the purpose of eliminating sulfur poisoning.
- An NOx selective catalytic reduction catalyst (hereinafter, also referred to as SCR catalyst) may be provided downstream of an NSR catalyst.
- the SCR catalyst is a catalyst that selectively reduces NOx with the use of a reducing agent.
- Ammonia is produced as a result of the reaction of HC or H 2 in exhaust gas with NOx in the NSR catalyst. The ammonia is allowed to be utilized as the reducing agent in the SCR catalyst.
- the internal combustion engine may be stopped in a state where the air-fuel ratio of the atmosphere in the SCR catalyst is a lean air-fuel ratio.
- ammonia adsorbed in the SCR catalyst is oxidized by oxygen in exhaust gas, with the result that NOx is produced.
- the NOx may be reduced by other ammonia adsorbed in the SCR catalyst. When such reactions are repeated, the amount of ammonia adsorbed in the SCR catalyst reduces.
- the phenomenon that the amount of ammonia adsorbed in the SCR catalyst reduces in this way is referred to as self-consumption.
- the amount of ammonia adsorbed in the SCR catalyst becomes deficient at the next start of the internal combustion engine because of the self-consumption of ammonia.
- Elimination of sulfur poisoning in the above-described related art is carried out through control for setting the air-fuel ratio in the NSR catalyst to a rich air-fuel ratio; however, the air-fuel ratio in the downstream SCR catalyst is not considered.
- the NOx purification performance of the SCR catalyst decreases because of a deficiency of ammonia adsorbed in the SCR catalyst.
- the teaching of the disclosure reduces or even eliminates a deficiency of ammonia adsorbed in an SCR catalyst at a start of an internal combustion engine.
- An aspect of the disclosure provides an exhaust gas control system for an internal combustion engine.
- the internal combustion engine is operable at a lean air-fuel ratio.
- the exhaust gas control system includes: an NOx selective catalytic reduction catalyst provided in an exhaust passage of the internal combustion engine, the NOx selective catalytic reduction catalyst being configured to adsorb ammonia and reduce NOx with the use of the adsorbed ammonia as a reducing agent; an air-fuel ratio control unit configured to change an air-fuel ratio in the internal combustion engine; and an engine stop control unit configured to, after a request to stop the internal combustion engine has been issued, until the air-fuel ratio in the NOx selective catalytic reduction catalyst becomes lower than or equal to a stoichiometric air-fuel ratio, cause the air-fuel ratio control unit to operate the internal combustion engine at the stoichiometric air-fuel ratio or lower, and then execute a stop control that is a control for stopping supply of fuel to the internal combustion engine.
- An exhaust gas control system for an internal combustion engine operable at a lean air-fuel ratio includes: an NOx selective catalytic reduction catalyst provided in an exhaust passage of the internal combustion engine, the NOx selective catalytic reduction catalyst being configured to adsorb ammonia and reduce NOx with the use of the adsorbed ammonia as a reducing agent; and an electronic control unit configured to i) change an air-fuel ratio in the internal combustion engine, ii) after a request to stop the internal combustion engine has been issued, until an air-fuel ratio in the NOx selective catalytic reduction catalyst becomes lower than or equal to a stoichiometric air-fuel ratio, operate the internal combustion engine at the stoichiometric air-fuel ratio or lower, and iii) after that, execute a stop control that is a control for stopping supply of fuel to the internal combustion engine.
- the exhaust gas control system may further include an upstream catalyst provided in the exhaust passage at a portion upstream of the NOx selective catalytic reduction catalyst, the upstream catalyst being a catalyst of which exhaust gas purification performance decreases because of hydrocarbon poisoning, and the engine stop control unit may be configured to, in the stop control, after causing the air-fuel ratio control unit to operate the internal combustion engine at the stoichiometric air-fuel ratio or lower until the air-fuel ratio in the NOx selective catalytic reduction catalyst becomes the stoichiometric air-fuel ratio or lower, cause the air-fuel ratio control unit to operate the internal combustion engine at the stoichiometric air-fuel ratio or higher until an air-fuel ratio in the upstream catalyst becomes higher than or equal to the stoichiometric air-fuel ratio while the air-fuel ratio in the NOx selective catalytic reduction catalyst remains at the stoichiometric air-fuel ratio or lower, and then stop supply of fuel to the internal combustion engine.
- the air-fuel ratio in the upstream catalyst located upstream of the SCR catalyst is also lower than or equal to the stoichiometric air-fuel ratio. Therefore, there is a concern that hydrocarbon poisoning occurs in the upstream catalyst.
- the internal combustion engine is operated at the stoichiometric air-fuel ratio or higher such that the air-fuel ratio in the upstream catalyst changes from the air-fuel ratio lower than or equal to the stoichiometric air-fuel ratio to the air-fuel ratio higher than or equal to the stoichiometric air-fuel ratio.
- the internal combustion engine is operated at the stoichiometric air-fuel ratio or higher such that the air-fuel ratio in the upstream catalyst changes from the air-fuel ratio lower than or equal to the stoichiometric air-fuel ratio to the air-fuel ratio higher than or equal to the stoichiometric air-fuel ratio.
- the internal combustion engine When the internal combustion engine is operated at a lean air-fuel ratio until the air-fuel ratio in the upstream catalyst becomes a lean air-fuel ratio, the internal combustion engine is stopped before the air-fuel ratio in the SCR catalyst becomes a lean air-fuel ratio.
- the internal combustion engine when the internal combustion engine is operated at the stoichiometric air-fuel ratio until the air-fuel ratio in the SCR catalyst becomes the stoichiometric air-fuel ratio, the air-fuel ratio in the upstream catalyst is also the stoichiometric air-fuel ratio. Therefore, in this case, the internal combustion engine may be immediately stopped when the air-fuel ratio in the SCR catalyst becomes the stoichiometric air-fuel ratio. In this way, it is possible to reduce or even eliminate the chance of a start of the internal combustion engine in a state where hydrocarbon poisoning is occurring in the upstream catalyst.
- the exhaust gas control system may further include an upstream catalyst provided in the exhaust passage at a portion upstream of the NOx selective catalytic reduction catalyst, the upstream catalyst being a catalyst of which exhaust gas purification performance decreases because of hydrocarbon poisoning, and the engine stop control unit may be configured to, in the stop control, after supply of fuel to the internal combustion engine is stopped, adjust a pumping loss of the internal combustion engine such that a total intake air amount of the internal combustion engine in a period from when a rotation speed of the internal combustion engine becomes zero becomes a predetermined air amount, the predetermined air amount being a total intake air amount that is required to bring an air-fuel ratio in the upstream catalyst to the stoichiometric air-fuel ratio or higher while the air-fuel ratio in the NOx selective catalytic reduction catalyst remains lower than or equal to the stoichiometric air-fuel ratio.
- the pumping loss it is possible to adjust the amount of air that is emitted from the internal combustion engine by the time the engine rotation speed becomes zero.
- the pumping loss is adjusted such that air that is emitted from the internal combustion engine passes through the upstream catalyst and does not reach the SCR catalyst, it is possible to reduce or even eliminate hydrocarbon poisoning of the upstream catalyst and self-consumption of ammonia in the SCR catalyst.
- the engine stop control unit may be configured to set the pumping loss such that the pumping loss when the predetermiend air amount is small is larger than the pumping loss when the predetermined air amount is large.
- the amount of air that is emitted from the internal combustion engine may be smaller. Because the engine rotation speed more early decreases as the pumping loss is increased, the amount of air that is emitted from the internal combustion engine by the time the engine rotation speed becomes zero reduces. Therefore, by increasing the pumping loss as the predetermined air amount reduces, it is possible to reduce or even eliminate an excess of air that is emitted from the internal combustion engine. On the other hand, when the predetermined air amount is large, it is possible to cause a large amount of air to be emitted from the internal combustion engine by the time the rotation speed of the internal combustion engine becomes zero by reducing the pumping loss, so it is possible to reduce or even eliminate a deficiency of air. In this way, by adjusting the pumping loss in response to the predetermined air amount, it is possible to reduce or even eliminate an excess or deficiency of air that is emitted from the internal combustion engine.
- the engine stop control unit may be configured to set the pumping loss such that the pumping loss when a temperature of the internal combustion engine is high is larger than the pumping loss when the temperature of the internal combustion engine is low.
- the engine rotation speed is more difficult to decrease when the temperature of the internal combustion engine is high than when the temperature of the internal combustion engine is low. Therefore, when the temperature of the internal combustion engine is high, there is a concern that the amount of air that is emitted from the internal combustion engine becomes excessive by the time the rotation speed of the internal combustion engine becomes zero. In this case, it is possible to quickly decrease the rotation speed of the internal combustion engine by increasing the pumping loss, so it is possible to reduce the amount of air that is emitted from the internal combustion engine. Therefore, it is possible to reduce or even eliminate an excess of air.
- the upstream catalyst may include at least one of a three-way catalyst and an NOx storage reduction catalyst.
- the three-way catalyst may be provided in the exhaust passage of the internal combustion engine, and may have an oxygen storage capability.
- the NOx storage reduction catalyst may be provided in the exhaust passage at a portion downstream of the three-way catalyst.
- the NOx storage reduction catalyst may store NOx when the air-fuel ratio is a lean air-fuel ratio, and reduce NOx when the air-fuel ratio is lower than or equal to the stoichiometric air-fuel ratio.
- ammonia is allowed to be produced in each of the three-way catalyst and the NSR catalyst, it is possible to supply ammonia to the SCR catalyst by providing the three-way catalyst and the NSR catalyst at a portion upstream of the SCR catalyst.
- the air-fuel ratio in each of the three-way catalyst and the NSR catalyst can also be lower than or equal to the stoichiometric air-fuel ratio. In this case, there is a concern that hydrocarbon poisoning occurs in these three-way catalyst and NSR catalyst.
- the engine stop control unit may be configured to, when a request to stop the internal combustion engine has been issued and when a condition for self-consumption of ammonia adsorbed in the NOx selective catalytic reduction catalyst is satisfied, execute the stop control.
- Self-consumption is a phenomenon that the amount of ammonia adsorbed in the SCR catalyst reduces as a result of the fact that ammonia adsorbed in the SCR catalyst is oxidized by oxygen in exhaust gas to produce NOx as described above and the NOx is reduced by other ammonia adsorbed in the SCR catalyst.
- the condition for self-consumption of ammonia adsorbed in the SCR catalyst is not satisfied, self-consumption of ammonia does not occur even when the internal combustion engine is stopped, so it is not necessary to operate the internal combustion engine at the stoichiometric air-fuel ratio or lower before supply of fuel to the internal combustion engine is stopped. In this case, by immediately stopping the internal combustion engine without executing the stop control, it is possible to reduce the consumption of fuel.
- the exhaust gas control system may further include an air-fuel ratio detection unit configured to detect or estimate the air-fuel ratio in the NOx selective catalytic reduction catalyst, and the engine stop control unit may be configured to, when the air-fuel ratio detected or estimated by the air-fuel ratio detection unit is a lean air-fuel ratio, determine that the condition for self-consumption of ammonia adsorbed in the NOx selective catalytic reduction catalyst is satisfied.
- an air-fuel ratio detection unit configured to detect or estimate the air-fuel ratio in the NOx selective catalytic reduction catalyst
- the engine stop control unit may be configured to, when the air-fuel ratio detected or estimated by the air-fuel ratio detection unit is a lean air-fuel ratio, determine that the condition for self-consumption of ammonia adsorbed in the NOx selective catalytic reduction catalyst is satisfied.
- the air-fuel ratio in the SCR catalyst becomes a lean air-fuel ratio, so self-consumption of ammonia occurs in the SCR catalyst.
- the air-fuel ratio that is detected or estimated by the air-fuel ratio detection unit is a lean air-fuel ratio. Therefore, when the air-fuel ratio detected or estimated by the air-fuel ratio detection unit is a lean air-fuel ratio, self-consumption can occur in the SCR catalyst.
- the air-fuel ratio that is detected or estimated by the air-fuel ratio detection unit becomes lower than or equal to the stoichiometric air-fuel ratio, so self-consumption of ammonia does not occur in the SCR catalyst. In this case, it is possible to immediately stop the internal combustion engine without executing the stop control.
- the exhaust gas control system may further include a temperature detection unit configured to detect or estimate a temperature in the NOx selective catalytic reduction catalyst, the engine stop control unit may be configured to, when the temperature detected or estimated by the temperature detection unit is higher than or equal to a lower limit temperature that is a temperature at which self-consumption of ammonia adsorbed in the NOx selective catalytic reduction catalyst begins, determine that the condition for self-consumption of ammonia adsorbed in the NOx selective catalytic reduction catalyst is satisfied.
- a temperature detection unit configured to detect or estimate a temperature in the NOx selective catalytic reduction catalyst
- the engine stop control unit may be configured to, when the temperature detected or estimated by the temperature detection unit is higher than or equal to a lower limit temperature that is a temperature at which self-consumption of ammonia adsorbed in the NOx selective catalytic reduction catalyst begins, determine that the condition for self-consumption of ammonia adsorbed in the NOx selective catalytic reduction catalyst is satisfied.
- the exhaust gas control system may further include a temperature detection unit configured to detect or estimate a temperature in the NOx selective catalytic reduction catalyst, and the engine stop control unit may be configured to, when the temperature detected or estimated by the temperature detection unit is lower than an upper limit temperature that is an upper limit value of a temperature at which ammonia remains in the NOx selective catalytic reduction catalyst, determine that the condition for self-consumption of ammonia adsorbed in the NOx selective catalytic reduction catalyst is satisfied.
- a temperature detection unit configured to detect or estimate a temperature in the NOx selective catalytic reduction catalyst
- the engine stop control unit may be configured to, when the temperature detected or estimated by the temperature detection unit is lower than an upper limit temperature that is an upper limit value of a temperature at which ammonia remains in the NOx selective catalytic reduction catalyst, determine that the condition for self-consumption of ammonia adsorbed in the NOx selective catalytic reduction catalyst is satisfied.
- the SCR catalyst When the temperature of the SCR catalyst is excessively high, the SCR catalyst is not able to adsorb ammonia any more, and ammonia desorbs from the SCR catalyst. Most of ammonia that has desorbed from the SCR catalyst flows out from the SCR catalyst. When the amount of ammonia that desorbs from the SCR catalyst per unit time becomes larger than the amount of ammonia that is adsorbed by the SCR catalyst per unit time, ammonia in the SCR catalyst reduces. That is, even when ammonia is supplied to the SCR catalyst, the amount of ammonia adsorbed in the SCR catalyst reduces.
- FIG. 1 is a view that shows the schematic configuration of an internal combustion engine according to the present embodiment and the schematic configurations of an intake system and exhaust system of the internal combustion engine.
- the internal combustion engine 1 shown in FIG. 1 is a gasoline engine.
- the internal combustion engine 1 is, for example, mounted on a vehicle.
- An exhaust pipe 72 is connected to the internal combustion engine 1.
- a three-way catalyst 31, an NOx storage reduction catalyst 32 (hereinafter, referred to as NSR catalyst 32), and an NOx selective catalytic reduction catalyst 33 (hereinafter, referred to as SCR catalyst 33) are provided in the exhaust pipe 72 in order from the upstream side.
- the three-way catalyst 31 purifies NOx, HC and CO when the atmosphere in the catalyst has a stoichiometric air-fuel ratio or an air-fuel ratio close to the stoichiometric air-fuel ratio.
- the three-way catalyst 31 has an oxygen storage capability. That is, excess oxygen is stored when the air-fuel ratio of exhaust gas flowing into the three-way catalyst 31 is a lean air-fuel ratio, and deficient oxygen is released when the air-fuel ratio of exhaust gas flowing into the three-way catalyst 31 is a rich air-fuel ratio. Thus, exhaust gas is purified.
- the three-way catalyst 31 is able to purify HC, CO and NOx even when the air-fuel ratio in the three-way catalyst 31 is an air-fuel ratio other than the stoichiometric air-fuel ratio.
- another catalyst for example, oxidation catalyst
- oxidation catalyst having an oxidation capability
- the NSR catalyst 32 stores NOx contained in exhaust gas when the concentration of oxygen in exhaust gas flowing into the NSR catalyst 32 is high, and reduces the stored NOx when the concentration of oxygen in exhaust gas flowing into the NSR catalyst 32 decreases and there is a reducing agent. That is, the NSR catalyst 32 stores NOx when the air-fuel ratio in the NSR catalyst 32 is a lean air-fuel ratio, and reduces NOx when the air-fuel ratio in the NSR catalyst 32 is lower than or equal to the stoichiometric air-fuel ratio.
- HC or CO that is unburned fuel emitted from the internal combustion engine 1 may be utilized as a reducing agent that is supplied to the NSR catalyst 32.
- NOx in exhaust gas may react with HC or H 2 to produce ammonia (NH 3 ).
- H 2 is produced from CO or H 2 O in exhaust gas as a result of water gas shift reaction or steam-reforming reaction
- the H 2 reacts with NOx in the three-way catalyst 31 or the NSR catalyst 32 to produce ammonia.
- Ammonia is produced when the air-fuel ratio of exhaust gas that passes through the three-way catalyst 31 or the NSR catalyst 32 is lower than or equal to the stoichiometric air-fuel ratio.
- the three-way catalyst 31 and the NSR catalyst 32 correspond to an upstream catalyst according to the disclosure.
- the SCR catalyst 33 adsorbs a reducing agent in advance, and, when NOx passes through the SCR catalyst 33, selectively reduces NOx with the use of the adsorbed reducing agent.
- Ammonia that is produced in the three-way catalyst 31 or the NSR catalyst 32 may be utilized as a reducing agent that is supplied to the SCR catalyst 33.
- a first air-fuel ratio sensor 91 is attached to the exhaust pipe 72 at a portion upstream of the three-way catalyst 31.
- the first air-fuel ratio sensor 91 detects the air-fuel ratio of exhaust gas.
- a second air-fuel ratio sensor 92 is attached to the exhaust pipe 72 at a portion downstream of the three-way catalyst 31 and upstream of the NSR catalyst 32.
- the second air-fuel ratio sensor 92 detects the air-fuel ratio of exhaust gas.
- a third air-fuel ratio sensor 93 is attached to the exhaust pipe 72 at a portion downstream of the NSR catalyst 32 and upstream of the SCR catalyst 33.
- the third air-fuel ratio sensor 93 detects the air-fuel ratio of exhaust gas.
- a fourth air-fuel ratio sensor 94 and an exhaust gas temperature sensor 99 are attached to the exhaust pipe 72 at a portion downstream of the SCR catalyst 33.
- the fourth air-fuel ratio sensor 94 detects the air-fuel ratio of exhaust gas.
- the exhaust gas temperature sensor 99 detects the temperature of exhaust gas.
- the temperature of the SCR catalyst 33 is allowed to be obtained from a detected value of the exhaust gas temperature sensor 99.
- An injection valve 83 is attached to the internal combustion engine 1.
- the injection valve 83 supplies fuel to the internal combustion engine 1.
- an intake pipe 42 is connected to the internal combustion engine 1.
- a throttle 16 is provided in the intake pipe 42. The throttle 16 adjusts the intake air amount of the internal combustion engine 1.
- An air flow meter 95 is attached to the intake pipe 42 at a portion upstream of the throttle 16. The air flow meter 95 detects the intake air amount of the internal combustion engine 1.
- An ECU 90 is provided in association with the internal combustion engine 1 configured as described above.
- the ECU 90 is an electronic control unit for controlling the internal combustion engine 1.
- the ECU 90 controls the internal combustion engine 1 in response to an operating condition of the internal combustion engine 1 or a driver's request.
- an accelerator operation amount sensor 97 and a crank position sensor 98 are connected to the ECU 90 via electrical lines, and output signals of these various sensors are input to the ECU 90.
- the accelerator operation amount sensor 97 detects an engine load by outputting an electrical signal corresponding to an amount by which the driver depresses an accelerator pedal.
- the crank position sensor 98 detects an engine rotation speed.
- the injection valve 83 and the throttle 16 are connected to the ECU 90 via electrical lines, and the open/close timing of the injection valve 83 and the opening degree of the throttle 16 are controlled by the ECU 90.
- An IG switch 20 is connected to the ECU 90. When the driver operates the IG switch 20, the ECU 90 starts or stops the internal combustion engine 1.
- the ECU 90 sets a target air-fuel ratio on the basis of the operating state (for example, the engine rotation speed and the accelerator operation amount) of the internal combustion engine 1.
- the throttle 16 or the injection valve 83 is controlled such that an actual air-fuel ratio becomes the target air-fuel ratio.
- Lean-burn operation that is, an operation at a lean air-fuel ratio
- the internal combustion engine 1 may be operated at an air-fuel ratio lower than or equal to the stoichiometric air-fuel ratio, for example, when the internal combustion engine 1 is cold started, when the engine operates at a high load, or when sulfur poisoning of the NSR catalyst 32 is eliminated.
- the ECU 90 that controls the air-fuel ratio corresponds to an air-fuel ratio control unit in the meaning of the disclosure.
- Ammonia adsorbed in the SCR catalyst 33 disappears through self-consumption of ammonia in the SCR catalyst 33.
- the self-consumption of ammonia is a phenomenon that ammonia adsorbed in the SCR catalyst 33 reacts with ambient oxygen to change into NOx and, in addition, ammonia is consumed in order for the NOx to react with ammonia adsorbed in the SCR catalyst 33.
- the ECU 90 sets the air-fuel ratio in the SCR catalyst 33 to a rich air-fuel ratio and then stops the internal combustion engine 1.
- a driver attempts to stop the internal combustion engine 1 by operating the IG switch 20, it is regarded that there is a request to stop the internal combustion engine 1 (a request to stop the internal combustion engine 1 has been issued).
- the ECU 90 causes the internal combustion engine 1 to operate at a rich air-fuel ratio.
- the SCR catalyst 33 is filled with exhaust gas when the internal combustion engine 1 is operated at a rich air-fuel ratio, that is, when the air-fuel ratio in the SCR catalyst 33 is a rich air-fuel ratio
- the ECU 90 stops supplying fuel to the internal combustion engine 1.
- Control for, after a request to stop the internal combustion engine 1 has been issued, operating the internal combustion engine 1 at a rich air-fuel ratio until the air-fuel ratio in the SCR catalyst 33 becomes a rich air-fuel ratio and then stopping supply of fuel to the internal combustion engine 1 is termed stop control.
- the air-fuel ratio in the SCR catalyst 33 is a rich air-fuel ratio.
- the air-fuel ratio of exhaust gas which is detected by the fourth air-fuel ratio sensor 94, is a rich air-fuel ratio
- the predetermined time may be obtained by an experiment, simulation, or the like, in advance as a time that is taken until the air-fuel ratio in the SCR catalyst 33 becomes a rich air-fuel ratio.
- the air-fuel ratio in the SCR catalyst 33 may be estimated on the basis of the operating state of the internal combustion engine 1.
- the fourth air-fuel ratio sensor 94 or the ECU 90 that estimates the air-fuel ratio in the SCR catalyst 33 corresponds to an air-fuel ratio detection unit in the meaning of the disclosure.
- FIG. 2 is a time chart that shows changes in various numeric values at the time of a stop of the internal combustion engine 1.
- the vehicle speed is the speed of the vehicle on which the internal combustion engine 1 is mounted.
- the engine output A/F is the air-fuel ratio of gas that is emitted from the internal combustion engine 1, and is the air-fuel ratio at the time of combustion in the internal combustion engine 1.
- the SCR output A/F is the air-fuel ratio of exhaust gas that flows out from the SCR catalyst 33, and is the air-fuel ratio of exhaust gas, which is detected by the fourth air-fuel ratio sensor 94.
- the continuous lines indicate the case where control according to the present embodiment is executed.
- the dashed lines indicate the case where existing control is executed for stopping the internal combustion engine 1 by stopping supply of fuel as soon as a request to stop the internal combustion engine 1 has been issued.
- the vehicle speed becomes 0.
- the internal combustion engine 1 is operated at idle, so the engine rotation speed is an idle rotation speed from T1.
- the internal combustion engine 1 is operated at the stoichiometric air-fuel ratio, so the engine output A/F becomes the stoichiometric air-fuel ratio.
- the IG switch 20 is turned off. That is, a request to stop the internal combustion engine 1 is issued at T2.
- the engine rotation speed begins to decrease from T2.
- the engine output A/F is higher than the stoichiometric air-fuel ratio from T2.
- the SCR output A/F remains at a lean air-fuel ratio and does not change.
- control is the same as the existing control until T2.
- the internal combustion engine 1 is operated at a rich air-fuel ratio from T2. That is, stop control is started from T2.
- the engine output A/F is a rich air-fuel ratio from T2; however, it takes time for exhaust gas having a rich air-fuel ratio to reach the SCR catalyst 33. Therefore, the SCR output A/F begins to decrease from T3, and the SCR output A/F becomes the stoichiometric air-fuel ratio at T4.
- the SCR catalyst 33 also has a certain oxygen storage capability, when exhaust gas having a rich air-fuel ratio flows into the SCR catalyst 33, oxygen is released from the SCR catalyst 33. While oxygen is being released, the air-fuel ratio in the SCR catalyst 33 is the stoichiometric air-fuel ratio.
- the SCR output A/F becomes lower than or equal to the stoichiometric air-fuel ratio
- supply of fuel is stopped in order to actually stop the internal combustion engine 1. That is, supply of fuel is stopped at T4, the engine rotation speed begins to decrease, and the engine output A/F becomes a lean air-fuel ratio.
- stopping the internal combustion engine 1 means stopping supply of fuel.
- stop control is executed in a period from T2 to T4. Because exhaust gas having a rich air-fuel ratio exists at a portion upstream of the SCR catalyst 33, exhaust gas having a rich air-fuel ratio is supplied to the SCR catalyst 33 until the rotation speed of the internal combustion engine 1 becomes zero even after T4. Oxygen that has been stored in the SCR catalyst 33 is empty at T5, and the SCR output A/F decreases from T5 to become a rich air-fuel ratio.
- FIG. 3 is a flowchart of control at the time of a stop of the internal combustion engine 1 according to the present embodiment.
- the flowchart is executed by the ECU 90 at predetermined time intervals during operation of the internal combustion engine 1.
- the ECU 90 that processes the flowchart corresponds to an engine stop control unit in the meaning of the disclosure.
- step S101 it is determined whether a request to stop the internal combustion engine 1 has been issued. That is, it is determined whether it is the time T2 in FIG. 2 . For example, when the IG switch 20 is in an off state, it is determined that a request to stop the internal combustion engine 1 has been issued.
- step S101 the process proceeds to step S102.
- step S101 the flowchart is ended.
- step S102 the internal combustion engine 1 is operated at a rich air-fuel ratio. That is, the target air-fuel ratio of the internal combustion engine 1 is set to a rich air-fuel ratio.
- the target air-fuel ratio at this time may be obtained in advance by an experiment, simulation, or the like.
- the engine output A/F is set to a rich air-fuel ratio.
- the air-fuel ratio of exhaust gas that flows through the exhaust pipe 72 sequentially becomes a rich air-fuel ratio from the internal combustion engine 1 side.
- step S103 it is determined whether the SCR output A/F is lower than or equal to the stoichiometric air-fuel ratio. That is, it is determined whether the air-fuel ratio in the SCR catalyst 33 is lower than or equal to the stoichiometric air-fuel ratio. This may be regarded as determining whether the time T3 in FIG. 2 has been reached. In this step, it is determined whether the operation at a rich air-fuel ratio is allowed to be terminated. It may be determined that the SCR output A/F is lower than or equal to the stoichiometric air-fuel ratio when the air-fuel ratio detected by the fourth air-fuel ratio sensor 94 is lower than or equal to the stoichiometric air-fuel ratio.
- step S103 it may be determined that the SCR output A/F is lower than or equal to the stoichiometric air-fuel ratio when the internal combustion engine 1 is operated at a rich air-fuel ratio for a predetermined time.
- estimate the SCR output A/F so it may be determined on the basis of the estimated value that the SCR output A/F is lower than or equal to the stoichiometric air-fuel ratio.
- step S104 stopping the internal combustion engine 1 is permitted.
- supply of fuel to the internal combustion engine 1 is stopped.
- the internal combustion engine 1 coasts; however, the rotation speed gradually decreases and finally becomes zero.
- the internal combustion engine 1 is operated at a rich air-fuel ratio in step S102 in order to promptly decrease the air-fuel ratio in the SCR catalyst 33.
- the internal combustion engine 1 may be operated at the stoichiometric air-fuel ratio.
- the internal combustion engine 1 is operated at the stoichiometric air-fuel ratio, it takes time; however, it is also possible to bring the air-fuel ratio in the SCR catalyst 33 to the stoichiometric air-fuel ratio.
- the air-fuel ratio in the SCR catalyst 33 is the stoichiometric air-fuel ratio, it is possible to suppress self-consumption of ammonia.
- the three-way catalyst 31 and the NSR catalyst 32 are not necessarily required.
- an ammonia addition valve that supplies ammonia to the SCR catalyst 33 is provided instead of the three-way catalyst 31 and the NSR catalyst 32, the three-way catalyst 31 and the NSR catalyst 32 may be omitted.
- the air-fuel ratio in the SCR catalyst 33 after a stop of the internal combustion engine 1 is lower than or equal to the stoichiometric air-fuel ratio, it is possible to suppress self-consumption of ammonia in the SCR catalyst 33 after a stop of the internal combustion engine 1.
- a condition for executing stop control is set.
- the other devices, and the like, are the same as those of the first embodiment, so the description thereof is omitted.
- Ammonia adsorbed in the SCR catalyst 33 also disappears not only through self-consumption but also through desorption of ammonia from the SCR catalyst 33.
- Desorption of ammonia is a phenomenon that ammonia desorbs from an adsorption site when the temperature of the SCR catalyst 33 is relatively high.
- FIG. 4 is a graph that shows the relationship between a temperature of the SCR catalyst 33 and a rate of disappearance of ammonia.
- the rate of disappearance of ammonia is the amount of ammonia that disappears from the SCR catalyst 33 per unit time.
- the continuous line in FIG. 4 indicates the rate of disappearance of ammonia through desorption of ammonia.
- the dashed line indicates the rate of disappearance of ammonia through self-consumption of ammonia.
- TA is a temperature (hereinafter, also referred to as lower limit temperature) at which self-consumption of ammonia begins.
- TB is an upper limit value of a temperature (hereinafter, also referred to as upper limit temperature) at which ammonia remains in the SCR catalyst 33.
- stop control when a request to stop the internal combustion engine 1 has been issued, and when the temperature of the SCR catalyst 33 is higher than or equal to the lower limit temperature TA and lower than or equal to the upper limit temperature TB, stop control is executed.
- stop control is executed when a request to stop the internal combustion engine 1 has been issued and when the temperature of the SCR catalyst 33 is higher than or equal to the lower limit temperature TA and lower than or equal to the upper limit temperature TB will be described.
- stop control when a request to stop the internal combustion engine 1 has been issued, and only when the air-fuel ratio in the SCR catalyst 33 is a lean air-fuel ratio, stop control is executed.
- the air-fuel ratio in the SCR catalyst 33 is not a lean air-fuel ratio, that is, the air-fuel ratio in the SCR catalyst 33 is the stoichiometric air-fuel ratio or a rich air-fuel ratio, because oxygen is almost not contained in exhaust gas, self-consumption of ammonia almost does not occur after a stop of the internal combustion engine 1. Therefore, it is not necessary to execute stop control. In this case as well, it is possible to reduce the consumption of fuel by quickly stopping the internal combustion engine 1.
- FIG. 5 is a flowchart of control at the time of a stop of the internal combustion engine 1 according to the present embodiment.
- the flowchart is executed by the ECU 90 at predetermined time intervals during operation of the internal combustion engine 1.
- Like step numbers denote steps of the same processes as those of the steps of the above-described flowchart, and the description thereof is omitted.
- the ECU 90 that processes the flowchart corresponds to an engine stop control unit in the meaning of the disclosure.
- step S201 it is determined whether the temperature of the SCR catalyst 33 is higher than or equal to the lower limit temperature TA and lower than or equal to the upper limit temperature TB. In this step, it is determined whether the temperature of the SCR catalyst 33 falls within the range in which self-consumption of ammonia occurs.
- the lower limit temperature TA is, for example, 350°C
- the upper limit temperature TB is, for example, 500°C.
- these values depend on the composition, and the like, of the SCR catalyst 33, so these values are obtained in advance by an experiment, simulation, or the like.
- the temperature of the SCR catalyst 33 is obtained by the use of the exhaust gas temperature sensor 99.
- the temperature of the SCR catalyst 33 may also be estimated on the basis of the operating state of the internal combustion engine 1.
- the exhaust gas temperature sensor 99 or the ECU 90 that estimates the temperature of the SCR catalyst 33 corresponds to a temperature detection unit in the meaning of the disclosure.
- step S202 it is determined whether the SCR output A/F is higher than the stoichiometric air-fuel ratio. That is, it is determined whether the air-fuel ratio in the SCR catalyst 33 is a lean air-fuel ratio. In this step, it is determined whether it is necessary to decrease the air-fuel ratio in the SCR catalyst 33 to an air-fuel ratio lower than or equal to the stoichiometric air-fuel ratio.
- step S102 the process proceeds to step S102.
- step S104 the process proceeds to step S104.
- stop control is executed when both the condition regarding the temperature of the SCR catalyst 33 and the condition regarding the air-fuel ratio in the SCR catalyst 33 are satisfied.
- the internal combustion engine 1 is operated at a rich air-fuel ratio when any one of the conditions is satisfied, it is also possible to reduce the consumption of fuel. That is, step S201 or step S202 may be omitted.
- stop control is executed when the temperature of the SCR catalyst 33 is higher than or equal to the lower limit temperature TA and lower than or equal to the upper limit temperature TB.
- stop control may be executed when the temperature of the SCR catalyst 33 is higher than or equal to the lower limit temperature TA even when the temperature of the SCR catalyst 33 is not lower than or equal to the upper limit temperature TB.
- stop control may be executed when the temperature of the SCR catalyst 33 is lower than or equal to the upper limit temperature TB even when the temperature of the SCR catalyst 33 is not higher than or equal to the lower limit temperature TA.
- stop control after the air-fuel ratio in the SCR catalyst 33 is brought to a rich air-fuel ratio before the internal combustion engine 1 is stopped, the internal combustion engine 1 is operated such that the air-fuel ratio in each of the three-way catalyst 31 and the NSR catalyst 32 is changed from a rich air-fuel ratio resulting from the previous process to an air-fuel ratio higher than or equal to the stoichiometric air-fuel ratio, and then supply of fuel to the internal combustion engine 1 is stopped. Thus, the internal combustion engine 1 is stopped.
- the three-way catalyst 31 and the NSR catalyst 32 are not indispensable components, but, in the present embodiment, at least one of the three-way catalyst 31 and the NSR catalyst 32 is an indispensable component. In the present embodiment, description will be made on the assumption that both the three-way catalyst 31 and the NSR catalyst 32 are provided.
- the air-fuel ratio in each of the three-way catalyst 31 and the NSR catalyst 32 also becomes a rich air-fuel ratio. Then, in each of the three-way catalyst 31 and the NSR catalyst 32, poisoning due to HC (hydrocarbons) (hydrocarbon poisoning) can occur. There is a concern that the purification performance of each of the three-way catalyst 31 and the NSR catalyst 32 decreases at the next start of the internal combustion engine 1 because of the hydrocarbon poisoning.
- the air-fuel ratio in the SCR catalyst 33 is brought to a rich air-fuel ratio, and then the air-fuel ratio in each of the three-way catalyst 31 and the NSR catalyst 32 is brought to an air-fuel ratio higher than or equal to the stoichiometric air-fuel ratio while the air-fuel ratio in the SCR catalyst 33 remains at a rich air-fuel ratio.
- the air-fuel ratio in the SCR catalyst 33 is brought to an air-fuel ratio higher than or equal to the stoichiometric air-fuel ratio while the air-fuel ratio in the SCR catalyst 33 remains at a rich air-fuel ratio.
- FIG. 6 is a flowchart that shows changes in various numeric values at the time of a stop of the internal combustion engine 1.
- the continuous lines indicate the case where control according to the present embodiment is executed.
- the dashed lines indicate the case where control according to the first embodiment or the second embodiment is executed.
- the three-way catalyst output A/F is the air-fuel ratio of exhaust gas that flows out from the three-way catalyst 31, and is the air-fuel ratio of exhaust gas, which is detected by the second air-fuel ratio sensor 92.
- the NSR output A/F is the air-fuel ratio of exhaust gas that flows out from the NSR catalyst 32, and is the air-fuel ratio of exhaust gas, which is detected by the third air-fuel ratio sensor 93.
- Like signs T1 to T5 in FIG. 6 denote the same times as those in FIG. 2 .
- the three-way catalyst output A/F is the stoichiometric air-fuel ratio while oxygen is being released from the three-way catalyst 31 before the three-way catalyst output A/F becomes a rich air-fuel ratio
- the NSR output A/F is the stoichiometric air-fuel ratio while oxygen is being released from the NSR catalyst 32 before the NSR output A/F becomes a rich air-fuel ratio.
- the internal combustion engine 1 is operated at the stoichiometric air-fuel ratio from T4.
- the engine output A/F becomes the stoichiometric air-fuel ratio after T4.
- the air-fuel ratio begins to rise, in order, in the three-way catalyst output A/F and then in the NSR output A/F.
- the NSR output A/F becomes the stoichiometric air-fuel ratio at T6
- supply of fuel to the internal combustion engine 1 is stopped.
- the air-fuel ratio in the SCR catalyst 33 is kept at a rich air-fuel ratio.
- stop control is executed in a period from T2 to T6.
- the engine output A/F is a lean air-fuel ratio from T6, and, when the exhaust gas reaches the three-way catalyst 31, the air-fuel ratio in the three-way catalyst 31 becomes a lean air-fuel ratio. Because the three-way catalyst 31 has an oxygen storage capability, the three-way catalyst output A/F can be the stoichiometric air-fuel ratio while the three-way catalyst 31 is storing oxygen just after T6.
- FIG. 7 is a flowchart of control at the time of a stop of the internal combustion engine 1 according to the present embodiment.
- the flowchart is executed by the ECU 90 at predetermined time intervals during operation of the internal combustion engine 1.
- Like step numbers denote steps of the same processes as those of the steps of the above-described flowchart, and the description thereof is omitted.
- the ECU 90 that processes the flowchart corresponds to an engine stop control unit in the meaning of the disclosure.
- step S301 the internal combustion engine 1 is operated at the stoichiometric air-fuel ratio.
- the air-fuel ratio of exhaust gas that flows through the exhaust pipe 72 sequentially becomes the stoichiometric air-fuel ratio from the internal combustion engine 1 side.
- step S302 it is determined whether the NSR output A/F is the stoichiometric air-fuel ratio. That is, it is determined whether the air-fuel ratio in the NSR catalyst 32 is the stoichiometric air-fuel ratio. In this step, it is determined whether T6 in FIG. 6 has been reached. The NSR output A/F is the air-fuel ratio that is detected by the third air-fuel ratio sensor 93. In this step, it is determined whether the operation of the internal combustion engine 1 at the stoichiometric air-fuel ratio is allowed to be terminated. When affirmative determination is made in step S302, the process proceeds to step S104. On the other hand, when negative determination is made in step S302, the process returns to step S301. That is, until the NSR output A/F becomes the stoichiometric air-fuel ratio, the operation of the internal combustion engine 1 at the stoichiometric air-fuel ratio is continued.
- step S303 it is determined whether the SCR output A/F is the stoichiometric air-fuel ratio. That is, in this step, it is determined whether the air-fuel ratio in the SCR catalyst 33 is not a rich air-fuel ratio.
- the air-fuel ratio in the SCR catalyst 33 is a rich air-fuel ratio, it is presumable that the internal combustion engine 1 has been operated at a rich air-fuel ratio, so it is presumable that the air-fuel ratio in each of the three-way catalyst 31 and the NSR catalyst 32 that are located upstream of the SCR catalyst 33 is also a rich air-fuel ratio.
- the air-fuel ratio in the SCR catalyst 33 is a rich air-fuel ratio
- the operation of the internal combustion engine 1 at a rich air-fuel ratio is not required.
- the process proceeds to step S301, and the internal combustion engine 1 is operated at the stoichiometric air-fuel ratio.
- the air-fuel ratio in the SCR catalyst 33 is the stoichiometric air-fuel ratio
- the internal combustion engine 1 has been operated at the stoichiometric air-fuel ratio, so it is presumable that the air-fuel ratio in each of the three-way catalyst 31 and the NSR catalyst 32 that are located upstream of the SCR catalyst 33 is also the stoichiometric air-fuel ratio.
- the internal combustion engine 1 is allowed to be stopped immediately without executing stop control, so the process proceeds to step S104.
- step S201 and step S202 may be omitted.
- step S303 may also be omitted.
- both the three-way catalyst 31 and the NSR catalyst 32 are provided. Instead, even when any one of the three-way catalyst 31 and the NSR catalyst 32 is provided, control is similarly handled. For example, when the three-way catalyst 31 is provided and the NSR catalyst 32 is not provided, it just needs to be determined in step S302 whether the three-way catalyst output A/F is the stoichiometric air-fuel ratio. In the present embodiment, the internal combustion engine 1 is operated at the stoichiometric air-fuel ratio in step S301.
- the internal combustion engine 1 may be operated at a lean air-fuel ratio.
- the internal combustion engine 1 When the internal combustion engine 1 is operated at a lean air-fuel ratio as well, it is possible to suppress hydrocarbon poisoning in the three-way catalyst 31 and the NSR catalyst 32.
- oxygen is excessive in the three-way catalyst 31 and the NSR catalyst 32, the purification performance decreases, so a certain air-fuel ratio may be obtained by an experiment, simulation, or the like.
- step S302 it may be determined that the NSR output A/F becomes the stoichiometric air-fuel ratio as a result of, for example, the fact that the internal combustion engine 1 has been operated at the stoichiometric air-fuel ratio for a predetermined time without utilizing the air-fuel ratio of exhaust gas, which is detected by the third air-fuel ratio sensor 93.
- the predetermined time may be obtained in advance by an experiment, simulation, or the like, as a time from when the operation of the internal combustion engine 1 at the stoichiometric air-fuel ratio is started to when the air-fuel ratio in the NSR catalyst 32 becomes the stoichiometric air-fuel ratio.
- stop control after a request to stop the internal combustion engine 1 has been issued, the internal combustion engine 1 is operated at a rich air-fuel ratio, and then the internal combustion engine 1 is operated at the stoichiometric air-fuel ratio in order to eliminate hydrocarbon poisoning.
- stop control after a request to stop the internal combustion engine 1 has been issued, the internal combustion engine 1 is operated at a rich air-fuel ratio, after that, supply of fuel is stopped without the operation of the internal combustion engine 1 at the stoichiometric air-fuel ratio, and oxygen is supplied to the three-way catalyst 31 and the NSR catalyst 32 in just proportion by adjusting the degree of decrease in the rotation speed of the internal combustion engine 1 until the rotation speed of the internal combustion engine 1 becomes zero.
- hydrocarbon poisoning of each of the three-way catalyst 31 and the NSR catalyst 32 is eliminated.
- FIG. 8 is a view that shows the schematic configuration of the internal combustion engine 1 according to the present embodiment and the schematic configurations of an intake system and exhaust system of the internal combustion engine 1. The difference from FIG. 1 will be mainly described.
- a cylinder head 10 of the internal combustion engine 1 has an intake port 41 and an exhaust port 71.
- the intake port 41 communicates the intake pipe 42 with a cylinder 2.
- the exhaust port 71 communicates the exhaust pipe 72 with the cylinder 2.
- An intake valve 5 is provided at the cylinder side end of the intake port 41.
- the intake valve 5 is opened or closed by an intake cam 6.
- An exhaust valve 9 is provided at the cylinder side end of the exhaust port 71.
- the exhaust valve 9 is opened or closed by an exhaust cam 11.
- the intake port 41 and the intake pipe 42 are included in an intake passage 4.
- the exhaust port 71 and the exhaust pipe 72 are included in an exhaust passage 7.
- the intake cam 6 is connected to an intake cam shaft 22, and an intake pulley 24 is provided at an end of the intake cam shaft 22.
- a variable rotation phase mechanism (hereinafter referred to as intake VVT) 23 is provided between the intake cam shaft 22 and the intake pulley 24.
- the intake VVT 23 is able to change a relative rotation phase between the intake cam shaft 22 and the intake pulley 24.
- the exhaust cam 11 is connected to an exhaust cam shaft 25, and an exhaust pulley 27 is provided at an end of the exhaust cam shaft 25.
- a variable rotation phase mechanism (hereinafter, referred to as exhaust VVT) 26 is provided between the exhaust cam shaft 25 and the exhaust pulley 27.
- the exhaust VVT 26 is able to change a relative rotation phase between the exhaust cam shaft 25 and the exhaust pulley 27.
- the intake pulley 24 and the exhaust pulley 27 rotate by driving force obtained from a crankshaft 13.
- the intake VVT 23 is able to change the open/close timing of the intake valve 5 by changing the relationship between a rotation angle of the crankshaft 13 and a rotation angle of the intake cam shaft 22.
- the exhaust VVT 26 is able to change the open/close timing of the exhaust valve 9 by changing the relationship between a rotation angle of the crankshaft 13 and a rotation angle of the exhaust cam shaft 25.
- a mechanism of changing the open/close timing of the intake valve 5 or the exhaust valve 9 is not limited to the above-described intake VVT 23 or exhaust VVT 26. Another mechanism may be used.
- a piston 15 coupled to the crankshaft 13 of the internal combustion engine 1 via a connecting rod 14 reciprocates inside the cylinder 2.
- a compressor 51 of a turbocharger 50 is provided in the intake pipe 42.
- the turbocharger 50 operates by using the energy of exhaust gas as a drive source.
- the throttle 16 is provided in the intake pipe 42 at a portion upstream of the compressor 51.
- a turbine 52 of the turbocharger 50 is provided in the exhaust pipe 72.
- a bypass passage 53 is provided so as to connect the exhaust pipe 72 at a portion upstream of the turbine 52 with the exhaust pipe 72 at a portion downstream of the turbine 52.
- a wastegate valve 54 is provided in the bypass passage 53. The wastegate valve 54 opens or closes the bypass passage 53.
- the first air-fuel ratio sensor 91 is provided in the exhaust pipe 72 at a portion downstream of the bypass passage 53.
- a coolant temperature sensor 96 is provided in the internal combustion engine 1.
- the coolant temperature sensor 96 detects the temperature of coolant of the internal combustion engine 1. It is possible to detect the temperature of the internal combustion engine 1 with the use of the coolant temperature sensor 96.
- a sensor that detects the temperature of lubricating oil instead of the temperature of coolant may be provided.
- the intake VVT 23, the exhaust VVT 26 and the wastegate valve 54 are connected to the ECU 90 via electrical lines. These devices are controlled by the ECU 90.
- the coolant temperature sensor 96 is connected to the ECU 90 via an electrical line. An output signal of the coolant temperature sensor 96 is input to the ECU 90.
- the ECU 90 adjusts a pumping loss of the internal combustion engine 1 such that the amount of gas that is emitted from the internal combustion engine 1 in a period from when supply of fuel to the internal combustion engine 1 is stopped to when the engine rotation speed becomes zero becomes the amount of gas by which hydrocarbon poisoning in the NSR catalyst 32 is eliminated.
- the pumping loss is adjustable by at least one of the throttle 16, the intake VVT 23, the exhaust VVT 26 and the wastegate valve 54.
- the pumping loss is adjusted such that an integrated amount (that is, a total amount) of gas that is emitted from the internal combustion engine 1 in a period from when supply of fuel to the internal combustion engine 1 is stopped to when the rotation speed of the internal combustion engine 1 becomes zero becomes the amount of gas, which corresponds to the volume of the exhaust passage 7 from an outlet of the cylinder 2 (that is, the boundary between the cylinder 2 and the exhaust port 71) to an inlet of the SCR catalyst 33. Because no fuel is supplied to the internal combustion engine 1, the integrated amount of gas that is emitted from the internal combustion engine 1 is equal to an integrated intake air amount of the internal combustion engine 1.
- the amount of gas which corresponds to the volume of the exhaust passage 7 from the outlet of the cylinder 2 to the inlet of the SCR catalyst 33, corresponds to a predetermined air amount in the meaning of the disclosure.
- the pumping loss when the opening degree of the throttle 16 is small is larger than the pumping loss when the opening degree of the throttle 16 is large.
- the pumping loss when the opening degree of the wastegate valve 54 is small is larger than the pumping loss when the opening degree of the wastegate valve 54 is large.
- the pumping loss increases as the timing at which the opening degree of each of the intake valve 5 and the exhaust valve 9 becomes largest is more shifted from the timing at which the speed of the piston 15 is highest.
- a time from when supply of fuel to the internal combustion engine 1 is stopped to when the rotation speed of the internal combustion engine 1 becomes zero is influenced by not only the pumping loss but also a friction loss. Because the friction loss increases as the temperature of the internal combustion engine 1 decreases, a time up to when the rotation speed of the internal combustion engine 1 becomes zero shortens.
- a coolant temperature is detected as the temperature of the internal combustion engine 1, and the pumping loss is adjusted in response to the coolant temperature.
- the pumping loss may be adjusted on the basis of only any one of the predetermined air amount and the coolant temperature.
- FIG. 9 is a graph that shows the relationship among a coolant temperature of the internal combustion engine 1, an integrated intake air amount (predetermined air amount) that is required from when supply of fuel to the internal combustion engine 1 is stopped to when the rotation speed of the internal combustion engine 1 becomes zero, and a required pumping loss.
- the required pumping loss is such a pumping loss that an integrated amount of gas that is emitted from the internal combustion engine 1 in a period from when supply of fuel to the internal combustion engine 1 is stopped to when the rotation speed of the internal combustion engine 1 becomes zero is equal to the amount of gas, which corresponds to the volume of the exhaust passage 7 from the outlet of the cylinder 2 to the inlet of the SCR catalyst 33.
- the predetermined air amount is a value corresponding to the volume of the exhaust passage 7 from the outlet of the cylinder 2 to the inlet of the SCR catalyst 33. This value may be obtained in advance.
- the coolant temperature may be obtained with the use of the coolant temperature sensor 96.
- the amount of oxygen which is required until the air-fuel ratio in the NSR catalyst 32 becomes the stoichiometric air-fuel ratio, varies depending on the oxygen storage capability of each of the three-way catalyst 31 and the NSR catalyst 32. Because the oxygen storage capability of each of the three-way catalyst 31 and the NSR catalyst 32 varies depending on degradation, or the like, the predetermined air amount may be changed in response to the oxygen storage capability of each of the three-way catalyst 31 and the NSR catalyst 32. However, in the present embodiment, for the purpose of providing simpler control, a change in the oxygen storage capability of each of the three-way catalyst 31 and the NSR catalyst 32 is not considered.
- the required pumping loss reduces. That is, as the predetermined air amount increases, it is required to operate the internal combustion engine 1 for a longer time, so the required pumping loss reduces. As the coolant temperature decreases, the required pumping loss reduces. That is, as the coolant temperature decreases, the friction loss increases, so the required pumping loss may be smaller.
- the relationship shown in FIG. 9 may be obtained in advance by an experiment, simulation, or the like.
- the required pumping loss is obtained by the use of the relationship shown in FIG. 9 , and an actual pumping loss is adjusted to the required pumping loss.
- the relationship among a required pumping loss, an opening degree of the throttle 16, an open/close timing of the intake valve 5, an open/close timing of the exhaust valve 9, and an opening degree of the wastegate valve 54 is obtained in advance by an experiment, simulation, or the like.
- a map for directly obtaining the opening degree of the throttle 16, the open/close timing of the intake valve 5, the open/close timing of the exhaust valve 9 and the opening degree of the wastegate valve 54 from a predetermined air amount and a coolant temperature without obtaining a required pumping loss may be prepared and stored in the ECU 90.
- FIG. 10 is a time chart that shows changes in various numeric values at the time of a stop of the internal combustion engine 1.
- the continuous lines indicate the case where control according to the present embodiment is executed.
- the dashed lines indicate the case where control according to the third embodiment is executed.
- the continuous lines and the dashed lines take the same paths until T4.
- FIG. 11 is a time chart that shows changes in engine rotation speed, throttle opening degree and wastegate valve opening degree at the time of a stop of the internal combustion engine 1.
- the continuous lines indicate the case where the required pumping loss is small, and the alternate long and short dashes lines indicate that the required pumping loss is large.
- Like signs T1 to T6 in FIG. 10 and FIG. 11 denote the same times as those in FIG. 6 .
- the SCR output A/F becomes the stoichiometric air-fuel ratio at T4
- supply of fuel to the internal combustion engine 1 is stopped in the present embodiment.
- the rotation speed of the internal combustion engine 1 decreases after T4; however, at least one of the opening degree of the throttle 16, the open/close timing of the intake valve 5, the open/close timing of the exhaust valve 9 and the opening degree of the wastegate valve 54 is set in response to the required pumping loss.
- the degree of decrease in engine rotation speed is adjusted, so the amount of air that is emitted to the exhaust pipe 72 is also adjusted.
- the pumping loss may be adjusted at T4 or may be adjusted before T4 or after T4.
- the pumping loss may be adjusted while fuel is supplied to the internal combustion engine 1. That is, even when the SCR output A/F becomes the stoichiometric air-fuel ratio, fuel for adjusting the pumping loss may be supplied.
- the NSR output A/F is the stoichiometric air-fuel ratio.
- the three-way catalyst 31 is almost filled with air, and the three-way catalyst output A/F is higher than the stoichiometric air-fuel ratio.
- air has not reached the SCR catalyst 33, so the SCR output A/F is a rich air-fuel ratio.
- FIG. 12 is a flowchart of control at the time of a stop of the internal combustion engine 1 according to the present embodiment.
- the flowchart is executed by the ECU 90 at predetermined time intervals during operation of the internal combustion engine 1.
- Like step numbers denote steps of the same processes as those of the steps of the above-described flowchart, and the description thereof is omitted.
- the ECU 90 that processes the flowchart corresponds to an engine stop control unit in the meaning of the disclosure.
- step S401 the required pumping loss is calculated.
- the required pumping loss is calculated on the basis of FIG. 9 from the coolant temperature and predetermined air amount of the internal combustion engine 1.
- step S402 the pumping loss is adjusted such that the required pumping loss that is calculated in step S401 is equal to an actual pumping loss.
- step S104 the process proceeds to step S104.
- at least one of step S201 and step S202 may be omitted.
- step S303 may also be omitted.
- the friction loss can change depending on the individual difference, aged degradation, and the like, of each device.
- the required pumping loss is obtained in accordance with the relationship shown in FIG. 9 , obtained in advance, the obtained required pumping loss may deviate from an actually required pumping loss.
- the air-fuel ratio in each catalyst may be detected, and the required pumping loss may be corrected on the basis of the detected results.
- the required pumping loss may be corrected by multiplying the required pumping loss by a predetermined coefficient or the required pumping loss may be corrected in response to an air-fuel ratio that is detected by the fourth air-fuel ratio sensor 94.
- the internal combustion engine 1 After the rotation speed of the internal combustion engine 1 becomes zero, when the air-fuel ratio in the three-way catalyst 31 is lower than or equal to the stoichiometric air-fuel ratio, the amount of air emitted from the internal combustion engine 1 after supply of fuel to the internal combustion engine 1 is stopped is deficient. In this case, the internal combustion engine 1 is allowed to be rotated longer by correcting the required pumping loss such that the required pumping loss becomes smaller, so it is possible to bring the air-fuel ratio in the three-way catalyst 31 to a lean air-fuel ratio. For example, the required pumping loss may be corrected by multiplying the required pumping loss by a predetermined coefficient or the required pumping loss may be corrected in response to an air-fuel ratio that is detected by the second air-fuel ratio sensor 92.
- the internal combustion engine 1 is allowed to be rotated longer by correcting the required pumping loss such that the required pumping loss becomes smaller, so it is possible to bring the air-fuel ratio in the NSR catalyst 32 to the stoichiometric air-fuel ratio or higher.
- the required pumping loss may be corrected by multiplying the required pumping loss by a predetermined coefficient or the required pumping loss may be corrected in response to an air-fuel ratio that is detected by the third air-fuel ratio sensor 93.
- FIG. 13 is a flowchart for correcting a required pumping loss. The flowchart is started when the rotation speed of the internal combustion engine 1 becomes zero.
- step S501 it is determined whether the SCR output A/F is lower than or equal to the stoichiometric air-fuel ratio. In this step, it is determined whether the air-fuel ratio in the SCR catalyst 33 is an appropriate value through stop control. When affirmative determination is made in step S501, the process proceeds to step S502. On the other hand, when negative determination is made in step S501, the process proceeds to step S506, and the pumping loss is increased.
- step S502 it is determined whether the three-way catalyst output A/F is higher than the stoichiometric air-fuel ratio. In this step, it is determined whether the air-fuel ratio in the three-way catalyst 31 is an appropriate value through stop control. When affirmative determination is made in step S502, the process proceeds to step S503. On the other hand, when negative determination is made in step S502, the process proceeds to step S505, and the pumping loss is reduced.
- step S503 it is determined whether the NSR output A/F is higher than or equal to the stoichiometric air-fuel ratio. In this step, it is determined whether the air-fuel ratio in the NSR catalyst 32 is an appropriate value through stop control. When affirmative determination is made in step S503, the process proceeds to step S504. On the other hand, when negative determination is made in step S503, the process proceeds to step S505, and the pumping loss is reduced.
- step S504 it is presumable that the required pumping loss is an appropriate value, so the flowchart is ended without correcting the required pumping loss.
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Abstract
Description
- The present disclosure relates to an exhaust gas control system for an internal combustion engine.
- There is known a technique for arranging an NOx storage reduction catalyst (hereinafter, also referred to as NSR catalyst) in an exhaust passage of an internal combustion engine. The NSR catalyst stores NOx contained in exhaust gas when the concentration of oxygen in exhaust gas flowing into the NSR catalyst is high, and reduces the stored NOx when the concentration of oxygen in exhaust gas flowing into the NSR catalyst is low and there is a reducing agent.
- Sulfur poisoning of the NSR catalyst occurs because of a sulfur component that is contained in fuel. There is known a technique for, when there is a request to stop an internal combustion engine, actually stopping the internal combustion engine after sulfur poisoning of the NSR catalyst is eliminated (see, for example,
Japanese Patent Application Publication No. 10-231720 JP 10-231720 A - An NOx selective catalytic reduction catalyst (hereinafter, also referred to as SCR catalyst) may be provided downstream of an NSR catalyst. The SCR catalyst is a catalyst that selectively reduces NOx with the use of a reducing agent. Ammonia is produced as a result of the reaction of HC or H2 in exhaust gas with NOx in the NSR catalyst. The ammonia is allowed to be utilized as the reducing agent in the SCR catalyst.
- In an internal combustion engine that is operating at an air-fuel ratio higher than a stoichiometric air-fuel ratio, that is, an internal combustion engine that is performing lean-burn operation, the internal combustion engine may be stopped in a state where the air-fuel ratio of the atmosphere in the SCR catalyst is a lean air-fuel ratio. In such a state, ammonia adsorbed in the SCR catalyst is oxidized by oxygen in exhaust gas, with the result that NOx is produced. The NOx may be reduced by other ammonia adsorbed in the SCR catalyst. When such reactions are repeated, the amount of ammonia adsorbed in the SCR catalyst reduces. Hereinafter, the phenomenon that the amount of ammonia adsorbed in the SCR catalyst reduces in this way is referred to as self-consumption. There is a concern that the amount of ammonia adsorbed in the SCR catalyst becomes deficient at the next start of the internal combustion engine because of the self-consumption of ammonia. Elimination of sulfur poisoning in the above-described related art is carried out through control for setting the air-fuel ratio in the NSR catalyst to a rich air-fuel ratio; however, the air-fuel ratio in the downstream SCR catalyst is not considered. Thus, at the next start of the internal combustion engine, there is a concern that the NOx purification performance of the SCR catalyst decreases because of a deficiency of ammonia adsorbed in the SCR catalyst.
- The teaching of the disclosure reduces or even eliminates a deficiency of ammonia adsorbed in an SCR catalyst at a start of an internal combustion engine.
- An aspect of the disclosure provides an exhaust gas control system for an internal combustion engine. The internal combustion engine is operable at a lean air-fuel ratio. The exhaust gas control system includes: an NOx selective catalytic reduction catalyst provided in an exhaust passage of the internal combustion engine, the NOx selective catalytic reduction catalyst being configured to adsorb ammonia and reduce NOx with the use of the adsorbed ammonia as a reducing agent; an air-fuel ratio control unit configured to change an air-fuel ratio in the internal combustion engine; and an engine stop control unit configured to, after a request to stop the internal combustion engine has been issued, until the air-fuel ratio in the NOx selective catalytic reduction catalyst becomes lower than or equal to a stoichiometric air-fuel ratio, cause the air-fuel ratio control unit to operate the internal combustion engine at the stoichiometric air-fuel ratio or lower, and then execute a stop control that is a control for stopping supply of fuel to the internal combustion engine. An aspect of the disclosure may also be defined as follows. An exhaust gas control system for an internal combustion engine operable at a lean air-fuel ratio includes: an NOx selective catalytic reduction catalyst provided in an exhaust passage of the internal combustion engine, the NOx selective catalytic reduction catalyst being configured to adsorb ammonia and reduce NOx with the use of the adsorbed ammonia as a reducing agent; and an electronic control unit configured to i) change an air-fuel ratio in the internal combustion engine, ii) after a request to stop the internal combustion engine has been issued, until an air-fuel ratio in the NOx selective catalytic reduction catalyst becomes lower than or equal to a stoichiometric air-fuel ratio, operate the internal combustion engine at the stoichiometric air-fuel ratio or lower, and iii) after that, execute a stop control that is a control for stopping supply of fuel to the internal combustion engine.
- Even when the air-fuel ratio in the SCR catalyst is a lean air-fuel ratio as a result of the fact that the internal combustion engine has been operated at a lean air-fuel ratio till then, it is possible to bring the air-fuel ratio in the SCR catalyst to the stoichiometric air-fuel ratio or lower by operating the internal combustion engine at the stoichiometric air-fuel ratio or lower before the internal combustion engine is stopped. Thus, it is possible to reduce or even eliminate self-consumption of ammonia. Therefore, it is possible to reduce or even eliminate a deficiency of ammonia adsorbed in the SCR catalyst at the start of the internal combustion engine.
- The exhaust gas control system may further include an upstream catalyst provided in the exhaust passage at a portion upstream of the NOx selective catalytic reduction catalyst, the upstream catalyst being a catalyst of which exhaust gas purification performance decreases because of hydrocarbon poisoning, and the engine stop control unit may be configured to, in the stop control, after causing the air-fuel ratio control unit to operate the internal combustion engine at the stoichiometric air-fuel ratio or lower until the air-fuel ratio in the NOx selective catalytic reduction catalyst becomes the stoichiometric air-fuel ratio or lower, cause the air-fuel ratio control unit to operate the internal combustion engine at the stoichiometric air-fuel ratio or higher until an air-fuel ratio in the upstream catalyst becomes higher than or equal to the stoichiometric air-fuel ratio while the air-fuel ratio in the NOx selective catalytic reduction catalyst remains at the stoichiometric air-fuel ratio or lower, and then stop supply of fuel to the internal combustion engine.
- When the internal combustion engine is operated at the stoichiometric air-fuel ratio or lower before supply of fuel to the internal combustion engine is stopped, the air-fuel ratio in the upstream catalyst located upstream of the SCR catalyst is also lower than or equal to the stoichiometric air-fuel ratio. Therefore, there is a concern that hydrocarbon poisoning occurs in the upstream catalyst. For this reason, after the air-fuel ratio in the SCR catalyst becomes lower than or equal to the stoichiometric air-fuel ratio, the internal combustion engine is operated at the stoichiometric air-fuel ratio or higher such that the air-fuel ratio in the upstream catalyst changes from the air-fuel ratio lower than or equal to the stoichiometric air-fuel ratio to the air-fuel ratio higher than or equal to the stoichiometric air-fuel ratio. Thus, it is possible to stop the internal combustion engine in a state where the air-fuel ratio in the upstream catalyst is higher than or equal to the stoichiometric air-fuel ratio. When the internal combustion engine is operated at a lean air-fuel ratio until the air-fuel ratio in the upstream catalyst becomes a lean air-fuel ratio, the internal combustion engine is stopped before the air-fuel ratio in the SCR catalyst becomes a lean air-fuel ratio. On the other hand, when the internal combustion engine is operated at the stoichiometric air-fuel ratio until the air-fuel ratio in the SCR catalyst becomes the stoichiometric air-fuel ratio, the air-fuel ratio in the upstream catalyst is also the stoichiometric air-fuel ratio. Therefore, in this case, the internal combustion engine may be immediately stopped when the air-fuel ratio in the SCR catalyst becomes the stoichiometric air-fuel ratio. In this way, it is possible to reduce or even eliminate the chance of a start of the internal combustion engine in a state where hydrocarbon poisoning is occurring in the upstream catalyst.
- The exhaust gas control system may further include an upstream catalyst provided in the exhaust passage at a portion upstream of the NOx selective catalytic reduction catalyst, the upstream catalyst being a catalyst of which exhaust gas purification performance decreases because of hydrocarbon poisoning, and the engine stop control unit may be configured to, in the stop control, after supply of fuel to the internal combustion engine is stopped, adjust a pumping loss of the internal combustion engine such that a total intake air amount of the internal combustion engine in a period from when a rotation speed of the internal combustion engine becomes zero becomes a predetermined air amount, the predetermined air amount being a total intake air amount that is required to bring an air-fuel ratio in the upstream catalyst to the stoichiometric air-fuel ratio or higher while the air-fuel ratio in the NOx selective catalytic reduction catalyst remains lower than or equal to the stoichiometric air-fuel ratio.
- After the air-fuel ratio in the SCR catalyst becomes lower than or equal to the stoichiometric air-fuel ratio, when the internal combustion engine is operated at the stoichiometric air-fuel ratio or higher such that the air-fuel ratio in the upstream catalyst is brought to the stoichiometric air-fuel ratio or higher, fuel is consumed. On the other hand, when supply of fuel is stopped after the air-fuel ratio in the SCR catalyst becomes lower than or equal to the stoichiometric air-fuel ratio, it is possible to reduce the consumption of fuel. After supply of fuel is stopped, the engine rotation speed decreases while air is emitted from the internal combustion engine. The degree of decrease in the engine rotation speed correlates with a pumping loss. Therefore, by adjusting the pumping loss, it is possible to adjust the amount of air that is emitted from the internal combustion engine by the time the engine rotation speed becomes zero. When the pumping loss is adjusted such that air that is emitted from the internal combustion engine passes through the upstream catalyst and does not reach the SCR catalyst, it is possible to reduce or even eliminate hydrocarbon poisoning of the upstream catalyst and self-consumption of ammonia in the SCR catalyst.
- The engine stop control unit may be configured to set the pumping loss such that the pumping loss when the predetermiend air amount is small is larger than the pumping loss when the predetermined air amount is large.
- As the predetermined air amount reduces, the amount of air that is emitted from the internal combustion engine may be smaller. Because the engine rotation speed more early decreases as the pumping loss is increased, the amount of air that is emitted from the internal combustion engine by the time the engine rotation speed becomes zero reduces. Therefore, by increasing the pumping loss as the predetermined air amount reduces, it is possible to reduce or even eliminate an excess of air that is emitted from the internal combustion engine. On the other hand, when the predetermined air amount is large, it is possible to cause a large amount of air to be emitted from the internal combustion engine by the time the rotation speed of the internal combustion engine becomes zero by reducing the pumping loss, so it is possible to reduce or even eliminate a deficiency of air. In this way, by adjusting the pumping loss in response to the predetermined air amount, it is possible to reduce or even eliminate an excess or deficiency of air that is emitted from the internal combustion engine.
- The engine stop control unit may be configured to set the pumping loss such that the pumping loss when a temperature of the internal combustion engine is high is larger than the pumping loss when the temperature of the internal combustion engine is low.
- The engine rotation speed is more difficult to decrease when the temperature of the internal combustion engine is high than when the temperature of the internal combustion engine is low. Therefore, when the temperature of the internal combustion engine is high, there is a concern that the amount of air that is emitted from the internal combustion engine becomes excessive by the time the rotation speed of the internal combustion engine becomes zero. In this case, it is possible to quickly decrease the rotation speed of the internal combustion engine by increasing the pumping loss, so it is possible to reduce the amount of air that is emitted from the internal combustion engine. Therefore, it is possible to reduce or even eliminate an excess of air. On the other hand, when the temperature of the internal combustion engine is low, the rotation speed of the internal combustion engine tends to decrease after supply of fuel is stopped, so there is a concern that the amount of air that is emitted from the internal combustion engine becomes deficient. In this case, it is possible to reduce or even eliminate a decrease in the rotation speed of the internal combustion engine by reducing the pumping loss, so it is possible to increase the amount of air that is emitted from the internal combustion engine. In this way, by adjusting the pumping loss in response to the temperature of the internal combustion engine, it is possible to reduce or even eliminate an excess or deficiency of air that is emitted from the internal combustion engine.
- The upstream catalyst may include at least one of a three-way catalyst and an NOx storage reduction catalyst. The three-way catalyst may be provided in the exhaust passage of the internal combustion engine, and may have an oxygen storage capability. The NOx storage reduction catalyst may be provided in the exhaust passage at a portion downstream of the three-way catalyst. The NOx storage reduction catalyst may store NOx when the air-fuel ratio is a lean air-fuel ratio, and reduce NOx when the air-fuel ratio is lower than or equal to the stoichiometric air-fuel ratio.
- Because ammonia is allowed to be produced in each of the three-way catalyst and the NSR catalyst, it is possible to supply ammonia to the SCR catalyst by providing the three-way catalyst and the NSR catalyst at a portion upstream of the SCR catalyst. By executing the stop control, the air-fuel ratio in each of the three-way catalyst and the NSR catalyst can also be lower than or equal to the stoichiometric air-fuel ratio. In this case, there is a concern that hydrocarbon poisoning occurs in these three-way catalyst and NSR catalyst. In contrast, when the air-fuel ratio in each of the three-way catalyst and the NSR catalyst is made higher than or equal to the stoichiometric air-fuel ratio at the time of a stop of the internal combustion engine, it is possible to reduce or even eliminate hydrocarbon poisoning. Therefore, it is possible to reduce or even eliminate a decrease in the purification performance of each of the three-way catalyst and the NSR catalyst at the next start of the internal combustion engine.
- The engine stop control unit may be configured to, when a request to stop the internal combustion engine has been issued and when a condition for self-consumption of ammonia adsorbed in the NOx selective catalytic reduction catalyst is satisfied, execute the stop control.
- Self-consumption is a phenomenon that the amount of ammonia adsorbed in the SCR catalyst reduces as a result of the fact that ammonia adsorbed in the SCR catalyst is oxidized by oxygen in exhaust gas to produce NOx as described above and the NOx is reduced by other ammonia adsorbed in the SCR catalyst. When the condition for self-consumption of ammonia adsorbed in the SCR catalyst is not satisfied, self-consumption of ammonia does not occur even when the internal combustion engine is stopped, so it is not necessary to operate the internal combustion engine at the stoichiometric air-fuel ratio or lower before supply of fuel to the internal combustion engine is stopped. In this case, by immediately stopping the internal combustion engine without executing the stop control, it is possible to reduce the consumption of fuel.
- The exhaust gas control system may further include an air-fuel ratio detection unit configured to detect or estimate the air-fuel ratio in the NOx selective catalytic reduction catalyst, and the engine stop control unit may be configured to, when the air-fuel ratio detected or estimated by the air-fuel ratio detection unit is a lean air-fuel ratio, determine that the condition for self-consumption of ammonia adsorbed in the NOx selective catalytic reduction catalyst is satisfied.
- When the internal combustion engine has been operated at a lean air-fuel ratio, the air-fuel ratio in the SCR catalyst becomes a lean air-fuel ratio, so self-consumption of ammonia occurs in the SCR catalyst. In such a state, the air-fuel ratio that is detected or estimated by the air-fuel ratio detection unit is a lean air-fuel ratio. Therefore, when the air-fuel ratio detected or estimated by the air-fuel ratio detection unit is a lean air-fuel ratio, self-consumption can occur in the SCR catalyst. On the other hand, when the internal combustion engine has been operated at the stoichiometric air-fuel ratio or lower, the air-fuel ratio that is detected or estimated by the air-fuel ratio detection unit becomes lower than or equal to the stoichiometric air-fuel ratio, so self-consumption of ammonia does not occur in the SCR catalyst. In this case, it is possible to immediately stop the internal combustion engine without executing the stop control.
- The exhaust gas control system may further include a temperature detection unit configured to detect or estimate a temperature in the NOx selective catalytic reduction catalyst, the engine stop control unit may be configured to, when the temperature detected or estimated by the temperature detection unit is higher than or equal to a lower limit temperature that is a temperature at which self-consumption of ammonia adsorbed in the NOx selective catalytic reduction catalyst begins, determine that the condition for self-consumption of ammonia adsorbed in the NOx selective catalytic reduction catalyst is satisfied.
- Because self-consumption of ammonia does not occur in the SCR catalyst when the temperature of the SCR catalyst is lower than the lower limit temperature, it may be determined that the condition for self-consumption of ammonia adsorbed in the SCR catalyst is not satisfied. Therefore, it is possible to immediately stop the internal combustion engine even without executing the stop control. On the other hand, when the temperature of the SCR catalyst is higher than or equal to the lower limit temperature, self-consumption of ammonia can occur. Therefore, it may be determined that the condition for self-consumption of ammonia adsorbed in the SCR catalyst is satisfied.
- The exhaust gas control system may further include a temperature detection unit configured to detect or estimate a temperature in the NOx selective catalytic reduction catalyst, and the engine stop control unit may be configured to, when the temperature detected or estimated by the temperature detection unit is lower than an upper limit temperature that is an upper limit value of a temperature at which ammonia remains in the NOx selective catalytic reduction catalyst, determine that the condition for self-consumption of ammonia adsorbed in the NOx selective catalytic reduction catalyst is satisfied.
- When the temperature of the SCR catalyst is excessively high, the SCR catalyst is not able to adsorb ammonia any more, and ammonia desorbs from the SCR catalyst. Most of ammonia that has desorbed from the SCR catalyst flows out from the SCR catalyst. When the amount of ammonia that desorbs from the SCR catalyst per unit time becomes larger than the amount of ammonia that is adsorbed by the SCR catalyst per unit time, ammonia in the SCR catalyst reduces. That is, even when ammonia is supplied to the SCR catalyst, the amount of ammonia adsorbed in the SCR catalyst reduces. At the time of a stop of the internal combustion engine, when the temperature of ammonia is higher than the upper limit temperature, because almost no ammonia is adsorbed in the SCR catalyst, almost no ammonia that is subjected to self-consumption is left. Therefore, when the temperature of the SCR catalyst is higher than the upper limit temperature, because no ammonia remains in the SCR catalyst, self-consumption of ammonia does not occur. Therefore, it may be determined that the condition for self-consumption of ammonia adsorbed in the SCR catalyst is not satisfied. In the case of such a temperature, it is not necessary to execute the stop control, so it is possible to immediately stop the internal combustion engine. On the other hand, when the temperature of the SCR catalyst is lower than or equal to the upper limit temperature, ammonia can remain in the SCR catalyst, so self-consumption of ammonia can occur. Therefore, it is possible to determine that the condition for self-consumption of ammonia adsorbed in the SCR catalyst is satisfied.
- According to the aspect of the disclosure, it is possible to reduce or even eliminate a deficiency of ammonia adsorbed in the SCR catalyst at the time of the start of the internal combustion engine.
- Features, advantages, and technical and industrial significance of exemplary embodiments will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:
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FIG. 1 is a view that shows the schematic configuration of an internal combustion engine according to first to third embodiments and the schematic configurations of an intake system and exhaust system of the internal combustion engine; -
FIG. 2 is a time chart that shows changes in various numeric values at the time of a stop of the internal combustion engine; -
FIG. 3 is a flowchart of control at the time of a stop of the internal combustion engine according to the first embodiment; -
FIG. 4 is a graph that shows the relationship between a temperature of an SCR catalyst and a rate of disappearance of ammonia; -
FIG. 5 is a flowchart of control at the time of a stop of the internal combustion engine according to the second embodiment; -
FIG. 6 is a time chart that shows changes in various numeric values at the time of a stop of the internal combustion engine; -
FIG. 7 is a flowchart of control at the time of a stop of the internal combustion engine according to the third embodiment; -
FIG. 8 is a view that shows the schematic configuration of an internal combustion engine according to a fourth embodiment and the schematic configurations of an intake system and exhaust system of the internal combustion engine; -
FIG. 9 is a graph that shows the relationship among a coolant temperature of the internal combustion engine, an integrated intake air amount (predetermined air amount) that is required from when supply of fuel to the internal combustion engine is stopped to when the rotation speed of the internal combustion engine becomes zero, and a required pumping loss; -
FIG. 10 is a time chart that shows changes in various numeric values at the time of a stop of the internal combustion engine; -
FIG. 11 is a time chart that shows changes in engine rotation speed, throttle opening degree and wastegate valve opening degree at the time of a stop of the internal combustion engine; -
FIG. 12 is a flowchart of control at the time of a stop of the internal combustion engine according to the fourth embodiment; and -
FIG. 13 is a flowchart for correcting a required pumping loss. - Hereinafter, a mode for carrying out the teaching of the disclosure will be exemplarily described in detail with reference to the accompanying drawings by way of embodiments. However, the scope of the invention is not intended to be limited to the dimensions, materials, shapes, relative arrangement, and the like, of components described in the embodiments unless otherwise specified.
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FIG. 1 is a view that shows the schematic configuration of an internal combustion engine according to the present embodiment and the schematic configurations of an intake system and exhaust system of the internal combustion engine. Theinternal combustion engine 1 shown inFIG. 1 is a gasoline engine. Theinternal combustion engine 1 is, for example, mounted on a vehicle. - An
exhaust pipe 72 is connected to theinternal combustion engine 1. A three-way catalyst 31, an NOx storage reduction catalyst 32 (hereinafter, referred to as NSR catalyst 32), and an NOx selective catalytic reduction catalyst 33 (hereinafter, referred to as SCR catalyst 33) are provided in theexhaust pipe 72 in order from the upstream side. - The three-
way catalyst 31 purifies NOx, HC and CO when the atmosphere in the catalyst has a stoichiometric air-fuel ratio or an air-fuel ratio close to the stoichiometric air-fuel ratio. The three-way catalyst 31 has an oxygen storage capability. That is, excess oxygen is stored when the air-fuel ratio of exhaust gas flowing into the three-way catalyst 31 is a lean air-fuel ratio, and deficient oxygen is released when the air-fuel ratio of exhaust gas flowing into the three-way catalyst 31 is a rich air-fuel ratio. Thus, exhaust gas is purified. With the above oxygen storage capability, the three-way catalyst 31 is able to purify HC, CO and NOx even when the air-fuel ratio in the three-way catalyst 31 is an air-fuel ratio other than the stoichiometric air-fuel ratio. Instead of the three-way catalyst 31, another catalyst (for example, oxidation catalyst) having an oxidation capability may be provided. - The
NSR catalyst 32 stores NOx contained in exhaust gas when the concentration of oxygen in exhaust gas flowing into theNSR catalyst 32 is high, and reduces the stored NOx when the concentration of oxygen in exhaust gas flowing into theNSR catalyst 32 decreases and there is a reducing agent. That is, theNSR catalyst 32 stores NOx when the air-fuel ratio in theNSR catalyst 32 is a lean air-fuel ratio, and reduces NOx when the air-fuel ratio in theNSR catalyst 32 is lower than or equal to the stoichiometric air-fuel ratio. HC or CO that is unburned fuel emitted from theinternal combustion engine 1 may be utilized as a reducing agent that is supplied to theNSR catalyst 32. - When exhaust gas passes through the three-
way catalyst 31 or theNSR catalyst 32, NOx in exhaust gas may react with HC or H2 to produce ammonia (NH3). For example, when H2 is produced from CO or H2O in exhaust gas as a result of water gas shift reaction or steam-reforming reaction, the H2 reacts with NOx in the three-way catalyst 31 or theNSR catalyst 32 to produce ammonia. Ammonia is produced when the air-fuel ratio of exhaust gas that passes through the three-way catalyst 31 or theNSR catalyst 32 is lower than or equal to the stoichiometric air-fuel ratio. In the embodiment, the three-way catalyst 31 and theNSR catalyst 32 correspond to an upstream catalyst according to the disclosure. - The
SCR catalyst 33 adsorbs a reducing agent in advance, and, when NOx passes through theSCR catalyst 33, selectively reduces NOx with the use of the adsorbed reducing agent. Ammonia that is produced in the three-way catalyst 31 or theNSR catalyst 32 may be utilized as a reducing agent that is supplied to theSCR catalyst 33. - A first air-
fuel ratio sensor 91 is attached to theexhaust pipe 72 at a portion upstream of the three-way catalyst 31. The first air-fuel ratio sensor 91 detects the air-fuel ratio of exhaust gas. A second air-fuel ratio sensor 92 is attached to theexhaust pipe 72 at a portion downstream of the three-way catalyst 31 and upstream of theNSR catalyst 32. The second air-fuel ratio sensor 92 detects the air-fuel ratio of exhaust gas. - A third air-
fuel ratio sensor 93 is attached to theexhaust pipe 72 at a portion downstream of theNSR catalyst 32 and upstream of theSCR catalyst 33. The third air-fuel ratio sensor 93 detects the air-fuel ratio of exhaust gas. A fourth air-fuel ratio sensor 94 and an exhaustgas temperature sensor 99 are attached to theexhaust pipe 72 at a portion downstream of theSCR catalyst 33. The fourth air-fuel ratio sensor 94 detects the air-fuel ratio of exhaust gas. The exhaustgas temperature sensor 99 detects the temperature of exhaust gas. The temperature of theSCR catalyst 33 is allowed to be obtained from a detected value of the exhaustgas temperature sensor 99. - An
injection valve 83 is attached to theinternal combustion engine 1. Theinjection valve 83 supplies fuel to theinternal combustion engine 1. On the other hand, anintake pipe 42 is connected to theinternal combustion engine 1. Athrottle 16 is provided in theintake pipe 42. Thethrottle 16 adjusts the intake air amount of theinternal combustion engine 1. Anair flow meter 95 is attached to theintake pipe 42 at a portion upstream of thethrottle 16. Theair flow meter 95 detects the intake air amount of theinternal combustion engine 1. - An
ECU 90 is provided in association with theinternal combustion engine 1 configured as described above. TheECU 90 is an electronic control unit for controlling theinternal combustion engine 1. TheECU 90 controls theinternal combustion engine 1 in response to an operating condition of theinternal combustion engine 1 or a driver's request. Other than the above-described sensors, an acceleratoroperation amount sensor 97 and a crankposition sensor 98 are connected to theECU 90 via electrical lines, and output signals of these various sensors are input to theECU 90. The acceleratoroperation amount sensor 97 detects an engine load by outputting an electrical signal corresponding to an amount by which the driver depresses an accelerator pedal. The crankposition sensor 98 detects an engine rotation speed. On the other hand, theinjection valve 83 and thethrottle 16 are connected to theECU 90 via electrical lines, and the open/close timing of theinjection valve 83 and the opening degree of thethrottle 16 are controlled by theECU 90. AnIG switch 20 is connected to theECU 90. When the driver operates theIG switch 20, theECU 90 starts or stops theinternal combustion engine 1. - The
ECU 90 sets a target air-fuel ratio on the basis of the operating state (for example, the engine rotation speed and the accelerator operation amount) of theinternal combustion engine 1. Thethrottle 16 or theinjection valve 83 is controlled such that an actual air-fuel ratio becomes the target air-fuel ratio. Lean-burn operation (that is, an operation at a lean air-fuel ratio) is performed in theinternal combustion engine 1 according to the present embodiment. However, theinternal combustion engine 1 may be operated at an air-fuel ratio lower than or equal to the stoichiometric air-fuel ratio, for example, when theinternal combustion engine 1 is cold started, when the engine operates at a high load, or when sulfur poisoning of theNSR catalyst 32 is eliminated. In the embodiment, theECU 90 that controls the air-fuel ratio corresponds to an air-fuel ratio control unit in the meaning of the disclosure. - Ammonia adsorbed in the
SCR catalyst 33 disappears through self-consumption of ammonia in theSCR catalyst 33. The self-consumption of ammonia is a phenomenon that ammonia adsorbed in theSCR catalyst 33 reacts with ambient oxygen to change into NOx and, in addition, ammonia is consumed in order for the NOx to react with ammonia adsorbed in theSCR catalyst 33. - For the purpose of suppressing self-consumption of ammonia, when a request to stop the
internal combustion engine 1 has been issued, theECU 90 sets the air-fuel ratio in theSCR catalyst 33 to a rich air-fuel ratio and then stops theinternal combustion engine 1. In the present embodiment, when a driver attempts to stop theinternal combustion engine 1 by operating theIG switch 20, it is regarded that there is a request to stop the internal combustion engine 1 (a request to stop theinternal combustion engine 1 has been issued). Other than the above, for example, when the drive mode of a hybrid vehicle changes from a mode in which the hybrid vehicle travels by using theinternal combustion engine 1 to a mode in which the hybrid vehicle travels by using a motor or when an idle stop is performed, it may be regarded that a request to stop theinternal combustion engine 1 has been issued. - Therefore, when a request to stop the
internal combustion engine 1 has been issued, before theECU 90 stops supplying fuel to theinternal combustion engine 1, theECU 90 causes theinternal combustion engine 1 to operate at a rich air-fuel ratio. When theSCR catalyst 33 is filled with exhaust gas when theinternal combustion engine 1 is operated at a rich air-fuel ratio, that is, when the air-fuel ratio in theSCR catalyst 33 is a rich air-fuel ratio, theECU 90 stops supplying fuel to theinternal combustion engine 1. Control for, after a request to stop theinternal combustion engine 1 has been issued, operating theinternal combustion engine 1 at a rich air-fuel ratio until the air-fuel ratio in theSCR catalyst 33 becomes a rich air-fuel ratio and then stopping supply of fuel to theinternal combustion engine 1 is termed stop control. There are some conceivable methods of determining that the air-fuel ratio in theSCR catalyst 33 is a rich air-fuel ratio. In the present embodiment, when the air-fuel ratio of exhaust gas, which is detected by the fourth air-fuel ratio sensor 94, is a rich air-fuel ratio, it is determined that the air-fuel ratio in theSCR catalyst 33 is a rich air-fuel ratio. Other than the above, for example, it may be determined that the air-fuel ratio in theSCR catalyst 33 is a rich air-fuel ratio as a result of the fact that theinternal combustion engine 1 is operated at a rich air-fuel ratio for a predetermined time. The predetermined time may be obtained by an experiment, simulation, or the like, in advance as a time that is taken until the air-fuel ratio in theSCR catalyst 33 becomes a rich air-fuel ratio. With the use of a known technique, the air-fuel ratio in theSCR catalyst 33 may be estimated on the basis of the operating state of theinternal combustion engine 1. In the embodiment, the fourth air-fuel ratio sensor 94 or theECU 90 that estimates the air-fuel ratio in theSCR catalyst 33 corresponds to an air-fuel ratio detection unit in the meaning of the disclosure. -
FIG. 2 is a time chart that shows changes in various numeric values at the time of a stop of theinternal combustion engine 1. The vehicle speed is the speed of the vehicle on which theinternal combustion engine 1 is mounted. The engine output A/F is the air-fuel ratio of gas that is emitted from theinternal combustion engine 1, and is the air-fuel ratio at the time of combustion in theinternal combustion engine 1. The SCR output A/F is the air-fuel ratio of exhaust gas that flows out from theSCR catalyst 33, and is the air-fuel ratio of exhaust gas, which is detected by the fourth air-fuel ratio sensor 94. The continuous lines indicate the case where control according to the present embodiment is executed. The dashed lines indicate the case where existing control is executed for stopping theinternal combustion engine 1 by stopping supply of fuel as soon as a request to stop theinternal combustion engine 1 has been issued. - Initially, the case where the existing control is executed will be described. At T1, the vehicle speed becomes 0. Thus, the
internal combustion engine 1 is operated at idle, so the engine rotation speed is an idle rotation speed from T1. During idle operation, theinternal combustion engine 1 is operated at the stoichiometric air-fuel ratio, so the engine output A/F becomes the stoichiometric air-fuel ratio. At T2, theIG switch 20 is turned off. That is, a request to stop theinternal combustion engine 1 is issued at T2. In the existing technique, in order to stop theinternal combustion engine 1 as soon as a request to stop theinternal combustion engine 1 has been issued, supply of fuel is stopped from T2. Therefore, the engine rotation speed begins to decrease from T2. Because supply of fuel is stopped from T2, the engine output A/F is higher than the stoichiometric air-fuel ratio from T2. In the existing case, because theinternal combustion engine 1 is immediately stopped, exhaust gas when theinternal combustion engine 1 is operating at the idle rotation speed does not reach theSCR catalyst 33, so the SCR output A/F remains at a lean air-fuel ratio and does not change. - Next, the case where control according to the present embodiment is executed will be described. The control is the same as the existing control until T2. When a request to stop the
internal combustion engine 1 is issued at T2, theinternal combustion engine 1 is operated at a rich air-fuel ratio from T2. That is, stop control is started from T2. The engine output A/F is a rich air-fuel ratio from T2; however, it takes time for exhaust gas having a rich air-fuel ratio to reach theSCR catalyst 33. Therefore, the SCR output A/F begins to decrease from T3, and the SCR output A/F becomes the stoichiometric air-fuel ratio at T4. Here, because theSCR catalyst 33 also has a certain oxygen storage capability, when exhaust gas having a rich air-fuel ratio flows into theSCR catalyst 33, oxygen is released from theSCR catalyst 33. While oxygen is being released, the air-fuel ratio in theSCR catalyst 33 is the stoichiometric air-fuel ratio. In the present embodiment, when the SCR output A/F becomes lower than or equal to the stoichiometric air-fuel ratio, supply of fuel is stopped in order to actually stop theinternal combustion engine 1. That is, supply of fuel is stopped at T4, the engine rotation speed begins to decrease, and the engine output A/F becomes a lean air-fuel ratio. Unless otherwise specified, stopping theinternal combustion engine 1 means stopping supply of fuel. In the present embodiment, stop control is executed in a period from T2 to T4. Because exhaust gas having a rich air-fuel ratio exists at a portion upstream of theSCR catalyst 33, exhaust gas having a rich air-fuel ratio is supplied to theSCR catalyst 33 until the rotation speed of theinternal combustion engine 1 becomes zero even after T4. Oxygen that has been stored in theSCR catalyst 33 is empty at T5, and the SCR output A/F decreases from T5 to become a rich air-fuel ratio. -
FIG. 3 is a flowchart of control at the time of a stop of theinternal combustion engine 1 according to the present embodiment. The flowchart is executed by theECU 90 at predetermined time intervals during operation of theinternal combustion engine 1. In the present embodiment, theECU 90 that processes the flowchart corresponds to an engine stop control unit in the meaning of the disclosure. - In step S101, it is determined whether a request to stop the
internal combustion engine 1 has been issued. That is, it is determined whether it is the time T2 inFIG. 2 . For example, when theIG switch 20 is in an off state, it is determined that a request to stop theinternal combustion engine 1 has been issued. When affirmative determination is made in step S101, the process proceeds to step S102. On the other hand, when negative determination is made in step S101, the flowchart is ended. - In step S102, the
internal combustion engine 1 is operated at a rich air-fuel ratio. That is, the target air-fuel ratio of theinternal combustion engine 1 is set to a rich air-fuel ratio. The target air-fuel ratio at this time may be obtained in advance by an experiment, simulation, or the like. Thus, as shown from T2 to T3 inFIG. 2 , the engine output A/F is set to a rich air-fuel ratio. Thus, the air-fuel ratio of exhaust gas that flows through theexhaust pipe 72 sequentially becomes a rich air-fuel ratio from theinternal combustion engine 1 side. - In step S103, it is determined whether the SCR output A/F is lower than or equal to the stoichiometric air-fuel ratio. That is, it is determined whether the air-fuel ratio in the
SCR catalyst 33 is lower than or equal to the stoichiometric air-fuel ratio. This may be regarded as determining whether the time T3 inFIG. 2 has been reached. In this step, it is determined whether the operation at a rich air-fuel ratio is allowed to be terminated. It may be determined that the SCR output A/F is lower than or equal to the stoichiometric air-fuel ratio when the air-fuel ratio detected by the fourth air-fuel ratio sensor 94 is lower than or equal to the stoichiometric air-fuel ratio. Alternatively, it may be determined that the SCR output A/F is lower than or equal to the stoichiometric air-fuel ratio when theinternal combustion engine 1 is operated at a rich air-fuel ratio for a predetermined time. In addition, it is also possible to estimate the SCR output A/F, so it may be determined on the basis of the estimated value that the SCR output A/F is lower than or equal to the stoichiometric air-fuel ratio. When affirmative determination is made in step S103, the time T4 inFIG. 2 has been reached, so the process proceeds to step S104. On the other hand, when negative determination is made in step S103, the process returns to step S102. That is, until the SCR output A/F becomes lower than or equal to the stoichiometric air-fuel ratio, the operation at a rich air-fuel ratio is continued. - In step S104, stopping the
internal combustion engine 1 is permitted. Thus, supply of fuel to theinternal combustion engine 1 is stopped. After that, theinternal combustion engine 1 coasts; however, the rotation speed gradually decreases and finally becomes zero. - In the flowchart shown in
FIG. 3 , theinternal combustion engine 1 is operated at a rich air-fuel ratio in step S102 in order to promptly decrease the air-fuel ratio in theSCR catalyst 33. Instead, theinternal combustion engine 1 may be operated at the stoichiometric air-fuel ratio. When theinternal combustion engine 1 is operated at the stoichiometric air-fuel ratio, it takes time; however, it is also possible to bring the air-fuel ratio in theSCR catalyst 33 to the stoichiometric air-fuel ratio. When the air-fuel ratio in theSCR catalyst 33 is the stoichiometric air-fuel ratio, it is possible to suppress self-consumption of ammonia. - In the present embodiment, the three-
way catalyst 31 and theNSR catalyst 32 are not necessarily required. For example, when an ammonia addition valve that supplies ammonia to theSCR catalyst 33 is provided instead of the three-way catalyst 31 and theNSR catalyst 32, the three-way catalyst 31 and theNSR catalyst 32 may be omitted. - In this way, because the air-fuel ratio in the
SCR catalyst 33 after a stop of theinternal combustion engine 1 is lower than or equal to the stoichiometric air-fuel ratio, it is possible to suppress self-consumption of ammonia in theSCR catalyst 33 after a stop of theinternal combustion engine 1. Thus, it is possible to suppress a reduction in the amount of adsorbed ammonia after a stop of theinternal combustion engine 1, so it is possible to suppress a decrease in the purification rate of NOx at the next start of theinternal combustion engine 1. - In the present embodiment, a condition for executing stop control is set. The other devices, and the like, are the same as those of the first embodiment, so the description thereof is omitted. In the present embodiment, it is determined whether to execute stop control on the basis of the temperature of the
SCR catalyst 33 or the air-fuel ratio in theSCR catalyst 33. - Ammonia adsorbed in the
SCR catalyst 33 also disappears not only through self-consumption but also through desorption of ammonia from theSCR catalyst 33. Desorption of ammonia is a phenomenon that ammonia desorbs from an adsorption site when the temperature of theSCR catalyst 33 is relatively high. - Even when the
internal combustion engine 1 is stopped and there is no NOx that flows into theSCR catalyst 33, desorption of ammonia and self-consumption of ammonia can occur.FIG. 4 is a graph that shows the relationship between a temperature of theSCR catalyst 33 and a rate of disappearance of ammonia. The rate of disappearance of ammonia is the amount of ammonia that disappears from theSCR catalyst 33 per unit time. The continuous line inFIG. 4 indicates the rate of disappearance of ammonia through desorption of ammonia. The dashed line indicates the rate of disappearance of ammonia through self-consumption of ammonia. - TA is a temperature (hereinafter, also referred to as lower limit temperature) at which self-consumption of ammonia begins. TB is an upper limit value of a temperature (hereinafter, also referred to as upper limit temperature) at which ammonia remains in the
SCR catalyst 33. When the temperature of theSCR catalyst 33 is higher than the upper limit temperature TB, the amount of ammonia that desorbs from theSCR catalyst 33 is larger than the amount of ammonia that is newly adsorbed in theSCR catalyst 33 even when ammonia is supplied, with the result that no ammonia remains in theSCR catalyst 33. As shown inFIG. 4 , self-consumption of ammonia begins from the lower limit temperature TA, and the rate of disappearance of ammonia through self-consumption of ammonia increases as the temperature rises. However, when the temperature of theSCR catalyst 33 is higher than the upper limit temperature TB, the influence of desorption of ammonia is larger than the influence of self-consumption of ammonia. When the temperature of theSCR catalyst 33 is higher than the upper limit temperature TB, even when ammonia is supplied to theSCR catalyst 33, ammonia desorbs from theSCR catalyst 33, so it becomes difficult to increase the amount of adsorbed ammonia. When no ammonia is adsorbed in theSCR catalyst 33, self-consumption of ammonia does not occur. That is, when the temperature of theSCR catalyst 33 is higher than or equal to the lower limit temperature and lower than or equal to the upper limit temperature, self-consumption of ammonia can occur. - As described above, in the present embodiment, when a request to stop the
internal combustion engine 1 has been issued, and when the temperature of theSCR catalyst 33 is higher than or equal to the lower limit temperature TA and lower than or equal to the upper limit temperature TB, stop control is executed. In the present embodiment, the case where stop control is executed when a request to stop theinternal combustion engine 1 has been issued and when the temperature of theSCR catalyst 33 is higher than or equal to the lower limit temperature TA and lower than or equal to the upper limit temperature TB will be described. - When the temperature of the
SCR catalyst 33 is lower than the lower limit temperature TA, self-consumption of ammonia almost does not occur in theSCR catalyst 33, so it is not necessary to execute stop control for suppressing self-consumption of ammonia. When the temperature of theSCR catalyst 33 is higher than the upper limit temperature TB, ammonia is almost not adsorbed in theSCR catalyst 33, so it is not necessary to execute stop control for suppressing self-consumption of ammonia. In this way, when it is not necessary to bring the air-fuel ratio in theSCR catalyst 33 to a rich air-fuel ratio, it is possible to reduce the consumption of fuel by quickly stopping theinternal combustion engine 1 without executing stop control. - In the present embodiment, when a request to stop the
internal combustion engine 1 has been issued, and only when the air-fuel ratio in theSCR catalyst 33 is a lean air-fuel ratio, stop control is executed. When the air-fuel ratio in theSCR catalyst 33 is not a lean air-fuel ratio, that is, the air-fuel ratio in theSCR catalyst 33 is the stoichiometric air-fuel ratio or a rich air-fuel ratio, because oxygen is almost not contained in exhaust gas, self-consumption of ammonia almost does not occur after a stop of theinternal combustion engine 1. Therefore, it is not necessary to execute stop control. In this case as well, it is possible to reduce the consumption of fuel by quickly stopping theinternal combustion engine 1. -
FIG. 5 is a flowchart of control at the time of a stop of theinternal combustion engine 1 according to the present embodiment. The flowchart is executed by theECU 90 at predetermined time intervals during operation of theinternal combustion engine 1. Like step numbers denote steps of the same processes as those of the steps of the above-described flowchart, and the description thereof is omitted. In the present embodiment, theECU 90 that processes the flowchart corresponds to an engine stop control unit in the meaning of the disclosure. - In the flowchart shown in
FIG. 5 , when affirmative determination is made in step S101, the process proceeds to step S201. In step S201, it is determined whether the temperature of theSCR catalyst 33 is higher than or equal to the lower limit temperature TA and lower than or equal to the upper limit temperature TB. In this step, it is determined whether the temperature of theSCR catalyst 33 falls within the range in which self-consumption of ammonia occurs. The lower limit temperature TA is, for example, 350°C, and the upper limit temperature TB is, for example, 500°C. However, these values depend on the composition, and the like, of theSCR catalyst 33, so these values are obtained in advance by an experiment, simulation, or the like. The temperature of theSCR catalyst 33 is obtained by the use of the exhaustgas temperature sensor 99. The temperature of theSCR catalyst 33 may also be estimated on the basis of the operating state of theinternal combustion engine 1. In the present embodiment, the exhaustgas temperature sensor 99 or theECU 90 that estimates the temperature of theSCR catalyst 33 corresponds to a temperature detection unit in the meaning of the disclosure. When affirmative determination is made in step S201, the process proceeds to step S202. On the other hand, when negative determination is made in step S201, the process proceeds to step S104. - In step S202, it is determined whether the SCR output A/F is higher than the stoichiometric air-fuel ratio. That is, it is determined whether the air-fuel ratio in the
SCR catalyst 33 is a lean air-fuel ratio. In this step, it is determined whether it is necessary to decrease the air-fuel ratio in theSCR catalyst 33 to an air-fuel ratio lower than or equal to the stoichiometric air-fuel ratio. When affirmative determination is made in step S202, the process proceeds to step S102. On the other hand, when negative determination is made in step S202, the process proceeds to step S104. - In this way, only when the air-fuel ratio in the
SCR catalyst 33 is a lean air-fuel ratio at which self-consumption of ammonia occurs and the temperature of theSCR catalyst 33 is a temperature at which the amount of adsorbed ammonia reduces, stop control is executed. Thus, it is possible to suppress the operation of theinternal combustion engine 1 more than necessary. Thus, it is possible to reduce the consumption of fuel. - In the present embodiment, stop control is executed when both the condition regarding the temperature of the
SCR catalyst 33 and the condition regarding the air-fuel ratio in theSCR catalyst 33 are satisfied. Instead, when theinternal combustion engine 1 is operated at a rich air-fuel ratio when any one of the conditions is satisfied, it is also possible to reduce the consumption of fuel. That is, step S201 or step S202 may be omitted. - In the present embodiment, stop control is executed when the temperature of the
SCR catalyst 33 is higher than or equal to the lower limit temperature TA and lower than or equal to the upper limit temperature TB. Instead, stop control may be executed when the temperature of theSCR catalyst 33 is higher than or equal to the lower limit temperature TA even when the temperature of theSCR catalyst 33 is not lower than or equal to the upper limit temperature TB. Alternatively, stop control may be executed when the temperature of theSCR catalyst 33 is lower than or equal to the upper limit temperature TB even when the temperature of theSCR catalyst 33 is not higher than or equal to the lower limit temperature TA. - In stop control according to the present embodiment, after the air-fuel ratio in the
SCR catalyst 33 is brought to a rich air-fuel ratio before theinternal combustion engine 1 is stopped, theinternal combustion engine 1 is operated such that the air-fuel ratio in each of the three-way catalyst 31 and theNSR catalyst 32 is changed from a rich air-fuel ratio resulting from the previous process to an air-fuel ratio higher than or equal to the stoichiometric air-fuel ratio, and then supply of fuel to theinternal combustion engine 1 is stopped. Thus, theinternal combustion engine 1 is stopped. In the above-described embodiment, the three-way catalyst 31 and theNSR catalyst 32 are not indispensable components, but, in the present embodiment, at least one of the three-way catalyst 31 and theNSR catalyst 32 is an indispensable component. In the present embodiment, description will be made on the assumption that both the three-way catalyst 31 and theNSR catalyst 32 are provided. - When the
internal combustion engine 1 is operated such that the air-fuel ratio in theSCR catalyst 33 becomes a rich air-fuel ratio as in the case of the first embodiment before theinternal combustion engine 1 is stopped, the air-fuel ratio in each of the three-way catalyst 31 and theNSR catalyst 32 also becomes a rich air-fuel ratio. Then, in each of the three-way catalyst 31 and theNSR catalyst 32, poisoning due to HC (hydrocarbons) (hydrocarbon poisoning) can occur. There is a concern that the purification performance of each of the three-way catalyst 31 and theNSR catalyst 32 decreases at the next start of theinternal combustion engine 1 because of the hydrocarbon poisoning. - On the other hand, in the present embodiment, before the
internal combustion engine 1 is stopped, initially, the air-fuel ratio in theSCR catalyst 33 is brought to a rich air-fuel ratio, and then the air-fuel ratio in each of the three-way catalyst 31 and theNSR catalyst 32 is brought to an air-fuel ratio higher than or equal to the stoichiometric air-fuel ratio while the air-fuel ratio in theSCR catalyst 33 remains at a rich air-fuel ratio. Thus, it is possible to start theinternal combustion engine 1 in a state where the purification performance of each of the three-way catalyst 31, theNSR catalyst 32 and theSCR catalyst 33 is high at the next start of theinternal combustion engine 1. When the air-fuel ratio in each of the three-way catalyst 31 and theNSR catalyst 32 is excessively high, there is a concern that the purification performance decreases, so an optimal value of the air-fuel ratio may be obtained in advance through an experiment, simulation, or the like. -
FIG. 6 is a flowchart that shows changes in various numeric values at the time of a stop of theinternal combustion engine 1. The continuous lines indicate the case where control according to the present embodiment is executed. The dashed lines indicate the case where control according to the first embodiment or the second embodiment is executed. The three-way catalyst output A/F is the air-fuel ratio of exhaust gas that flows out from the three-way catalyst 31, and is the air-fuel ratio of exhaust gas, which is detected by the second air-fuel ratio sensor 92. The NSR output A/F is the air-fuel ratio of exhaust gas that flows out from theNSR catalyst 32, and is the air-fuel ratio of exhaust gas, which is detected by the third air-fuel ratio sensor 93. Like signs T1 to T5 inFIG. 6 denote the same times as those inFIG. 2 . - The continuous lines and the dashed lines take the same paths until T4. After the engine output A/F becomes a rich air-fuel ratio at T2, the air-fuel ratio in the upstreammost three-
way catalyst 31 becomes a rich air-fuel ratio first, and then the air-fuel ratio in theNSR catalyst 32 and the air-fuel ratio in theSCR catalyst 33 become a rich air-fuel ratio in this order. Because the three-way catalyst 31 and theNSR catalyst 32 each have an oxygen storage capability, the three-way catalyst output A/F is the stoichiometric air-fuel ratio while oxygen is being released from the three-way catalyst 31 before the three-way catalyst output A/F becomes a rich air-fuel ratio, and the NSR output A/F is the stoichiometric air-fuel ratio while oxygen is being released from theNSR catalyst 32 before the NSR output A/F becomes a rich air-fuel ratio. In the present embodiment, different from the first embodiment or the second embodiment, theinternal combustion engine 1 is operated at the stoichiometric air-fuel ratio from T4. Thus, the engine output A/F becomes the stoichiometric air-fuel ratio after T4. After that, the air-fuel ratio begins to rise, in order, in the three-way catalyst output A/F and then in the NSR output A/F. When the NSR output A/F becomes the stoichiometric air-fuel ratio at T6, supply of fuel to theinternal combustion engine 1 is stopped. In this case, because exhaust gas having the stoichiometric air-fuel ratio does not reach theSCR catalyst 33, the air-fuel ratio in theSCR catalyst 33 is kept at a rich air-fuel ratio. When the distance between theNSR catalyst 32 and theSCR catalyst 33 is short, exhaust gas having the stoichiometric air-fuel ratio can reach theSCR catalyst 33 by the time the rotation speed of theinternal combustion engine 1 becomes zero, so the air-fuel ratio in theSCR catalyst 33 may rise. However, because the air-fuel ratio of exhaust gas is the stoichiometric air-fuel ratio, self-consumption of ammonia in theSCR catalyst 33 is suppressed. In the present embodiment, stop control is executed in a period from T2 to T6. - Supply of fuel to the
internal combustion engine 1 is stopped from T6; however, gas is emitted from theinternal combustion engine 1 until the rotation speed of theinternal combustion engine 1 becomes zero. That is, the engine output A/F is a lean air-fuel ratio from T6, and, when the exhaust gas reaches the three-way catalyst 31, the air-fuel ratio in the three-way catalyst 31 becomes a lean air-fuel ratio. Because the three-way catalyst 31 has an oxygen storage capability, the three-way catalyst output A/F can be the stoichiometric air-fuel ratio while the three-way catalyst 31 is storing oxygen just after T6. -
FIG. 7 is a flowchart of control at the time of a stop of theinternal combustion engine 1 according to the present embodiment. The flowchart is executed by theECU 90 at predetermined time intervals during operation of theinternal combustion engine 1. Like step numbers denote steps of the same processes as those of the steps of the above-described flowchart, and the description thereof is omitted. In the present embodiment, theECU 90 that processes the flowchart corresponds to an engine stop control unit in the meaning of the disclosure. - In the flowchart shown in
FIG. 7 , when affirmative determination is made in step S103, the process proceeds to step S301. In step S301, theinternal combustion engine 1 is operated at the stoichiometric air-fuel ratio. Thus, the air-fuel ratio of exhaust gas that flows through theexhaust pipe 72 sequentially becomes the stoichiometric air-fuel ratio from theinternal combustion engine 1 side. - In step S302, it is determined whether the NSR output A/F is the stoichiometric air-fuel ratio. That is, it is determined whether the air-fuel ratio in the
NSR catalyst 32 is the stoichiometric air-fuel ratio. In this step, it is determined whether T6 inFIG. 6 has been reached. The NSR output A/F is the air-fuel ratio that is detected by the third air-fuel ratio sensor 93. In this step, it is determined whether the operation of theinternal combustion engine 1 at the stoichiometric air-fuel ratio is allowed to be terminated. When affirmative determination is made in step S302, the process proceeds to step S104. On the other hand, when negative determination is made in step S302, the process returns to step S301. That is, until the NSR output A/F becomes the stoichiometric air-fuel ratio, the operation of theinternal combustion engine 1 at the stoichiometric air-fuel ratio is continued. - In the flowchart shown in
FIG. 7 , when negative determination is made in step S202, the process proceeds to step S303. In step S303, it is determined whether the SCR output A/F is the stoichiometric air-fuel ratio. That is, in this step, it is determined whether the air-fuel ratio in theSCR catalyst 33 is not a rich air-fuel ratio. When the air-fuel ratio in theSCR catalyst 33 is a rich air-fuel ratio, it is presumable that theinternal combustion engine 1 has been operated at a rich air-fuel ratio, so it is presumable that the air-fuel ratio in each of the three-way catalyst 31 and theNSR catalyst 32 that are located upstream of theSCR catalyst 33 is also a rich air-fuel ratio. When the air-fuel ratio in theSCR catalyst 33 is a rich air-fuel ratio, the operation of theinternal combustion engine 1 at a rich air-fuel ratio is not required. However, because there is a concern that hydrocarbon poisoning is occurring in the three-way catalyst 31 and theNSR catalyst 32, when the SCR output A/F is a rich air-fuel ratio, the process proceeds to step S301, and theinternal combustion engine 1 is operated at the stoichiometric air-fuel ratio. - On the other hand, when the air-fuel ratio in the
SCR catalyst 33 is the stoichiometric air-fuel ratio, it is presumable that theinternal combustion engine 1 has been operated at the stoichiometric air-fuel ratio, so it is presumable that the air-fuel ratio in each of the three-way catalyst 31 and theNSR catalyst 32 that are located upstream of theSCR catalyst 33 is also the stoichiometric air-fuel ratio. In this case, theinternal combustion engine 1 is allowed to be stopped immediately without executing stop control, so the process proceeds to step S104. - As in the case of the first embodiment, at least one of step S201 and step S202 may be omitted. When step S202 is omitted, step S303 may also be omitted. In the present embodiment, both the three-
way catalyst 31 and theNSR catalyst 32 are provided. Instead, even when any one of the three-way catalyst 31 and theNSR catalyst 32 is provided, control is similarly handled. For example, when the three-way catalyst 31 is provided and theNSR catalyst 32 is not provided, it just needs to be determined in step S302 whether the three-way catalyst output A/F is the stoichiometric air-fuel ratio. In the present embodiment, theinternal combustion engine 1 is operated at the stoichiometric air-fuel ratio in step S301. Instead, theinternal combustion engine 1 may be operated at a lean air-fuel ratio. When theinternal combustion engine 1 is operated at a lean air-fuel ratio as well, it is possible to suppress hydrocarbon poisoning in the three-way catalyst 31 and theNSR catalyst 32. However, when oxygen is excessive in the three-way catalyst 31 and theNSR catalyst 32, the purification performance decreases, so a certain air-fuel ratio may be obtained by an experiment, simulation, or the like. - In step S302, it may be determined that the NSR output A/F becomes the stoichiometric air-fuel ratio as a result of, for example, the fact that the
internal combustion engine 1 has been operated at the stoichiometric air-fuel ratio for a predetermined time without utilizing the air-fuel ratio of exhaust gas, which is detected by the third air-fuel ratio sensor 93. The predetermined time may be obtained in advance by an experiment, simulation, or the like, as a time from when the operation of theinternal combustion engine 1 at the stoichiometric air-fuel ratio is started to when the air-fuel ratio in theNSR catalyst 32 becomes the stoichiometric air-fuel ratio. - As described above, according to the present embodiment, it is possible to suppress self-consumption of ammonia in the
SCR catalyst 33 and to suppress hydrocarbon poisoning in the three-way catalyst 31 and theNSR catalyst 32, so it is possible to further raise the purification performance of exhaust gas at the next start of theinternal combustion engine 1. - In stop control according to the third embodiment, after a request to stop the
internal combustion engine 1 has been issued, theinternal combustion engine 1 is operated at a rich air-fuel ratio, and then theinternal combustion engine 1 is operated at the stoichiometric air-fuel ratio in order to eliminate hydrocarbon poisoning. On the other hand, in stop control according to the present embodiment, after a request to stop theinternal combustion engine 1 has been issued, theinternal combustion engine 1 is operated at a rich air-fuel ratio, after that, supply of fuel is stopped without the operation of theinternal combustion engine 1 at the stoichiometric air-fuel ratio, and oxygen is supplied to the three-way catalyst 31 and theNSR catalyst 32 in just proportion by adjusting the degree of decrease in the rotation speed of theinternal combustion engine 1 until the rotation speed of theinternal combustion engine 1 becomes zero. Thus, hydrocarbon poisoning of each of the three-way catalyst 31 and theNSR catalyst 32 is eliminated. -
FIG. 8 is a view that shows the schematic configuration of theinternal combustion engine 1 according to the present embodiment and the schematic configurations of an intake system and exhaust system of theinternal combustion engine 1. The difference fromFIG. 1 will be mainly described. Acylinder head 10 of theinternal combustion engine 1 has anintake port 41 and anexhaust port 71. Theintake port 41 communicates theintake pipe 42 with acylinder 2. Theexhaust port 71 communicates theexhaust pipe 72 with thecylinder 2. Anintake valve 5 is provided at the cylinder side end of theintake port 41. Theintake valve 5 is opened or closed by anintake cam 6. Anexhaust valve 9 is provided at the cylinder side end of theexhaust port 71. Theexhaust valve 9 is opened or closed by anexhaust cam 11. Theintake port 41 and theintake pipe 42 are included in anintake passage 4. Theexhaust port 71 and theexhaust pipe 72 are included in anexhaust passage 7. - The
intake cam 6 is connected to anintake cam shaft 22, and anintake pulley 24 is provided at an end of theintake cam shaft 22. A variable rotation phase mechanism (hereinafter referred to as intake VVT) 23 is provided between theintake cam shaft 22 and theintake pulley 24. Theintake VVT 23 is able to change a relative rotation phase between theintake cam shaft 22 and theintake pulley 24. - The
exhaust cam 11 is connected to an exhaust cam shaft 25, and anexhaust pulley 27 is provided at an end of the exhaust cam shaft 25. A variable rotation phase mechanism (hereinafter, referred to as exhaust VVT) 26 is provided between the exhaust cam shaft 25 and theexhaust pulley 27. Theexhaust VVT 26 is able to change a relative rotation phase between the exhaust cam shaft 25 and theexhaust pulley 27. - The
intake pulley 24 and theexhaust pulley 27 rotate by driving force obtained from acrankshaft 13. Theintake VVT 23 is able to change the open/close timing of theintake valve 5 by changing the relationship between a rotation angle of thecrankshaft 13 and a rotation angle of theintake cam shaft 22. Theexhaust VVT 26 is able to change the open/close timing of theexhaust valve 9 by changing the relationship between a rotation angle of thecrankshaft 13 and a rotation angle of the exhaust cam shaft 25. A mechanism of changing the open/close timing of theintake valve 5 or theexhaust valve 9 is not limited to the above-describedintake VVT 23 orexhaust VVT 26. Another mechanism may be used. - A
piston 15 coupled to thecrankshaft 13 of theinternal combustion engine 1 via a connectingrod 14 reciprocates inside thecylinder 2. Acompressor 51 of aturbocharger 50 is provided in theintake pipe 42. Theturbocharger 50 operates by using the energy of exhaust gas as a drive source. Thethrottle 16 is provided in theintake pipe 42 at a portion upstream of thecompressor 51. - On the other hand, a
turbine 52 of theturbocharger 50 is provided in theexhaust pipe 72. Abypass passage 53 is provided so as to connect theexhaust pipe 72 at a portion upstream of theturbine 52 with theexhaust pipe 72 at a portion downstream of theturbine 52. Awastegate valve 54 is provided in thebypass passage 53. Thewastegate valve 54 opens or closes thebypass passage 53. The first air-fuel ratio sensor 91 is provided in theexhaust pipe 72 at a portion downstream of thebypass passage 53. - A
coolant temperature sensor 96 is provided in theinternal combustion engine 1. Thecoolant temperature sensor 96 detects the temperature of coolant of theinternal combustion engine 1. It is possible to detect the temperature of theinternal combustion engine 1 with the use of thecoolant temperature sensor 96. A sensor that detects the temperature of lubricating oil instead of the temperature of coolant may be provided. Theintake VVT 23, theexhaust VVT 26 and thewastegate valve 54 are connected to theECU 90 via electrical lines. These devices are controlled by theECU 90. Thecoolant temperature sensor 96 is connected to theECU 90 via an electrical line. An output signal of thecoolant temperature sensor 96 is input to theECU 90. - The
ECU 90 adjusts a pumping loss of theinternal combustion engine 1 such that the amount of gas that is emitted from theinternal combustion engine 1 in a period from when supply of fuel to theinternal combustion engine 1 is stopped to when the engine rotation speed becomes zero becomes the amount of gas by which hydrocarbon poisoning in theNSR catalyst 32 is eliminated. The pumping loss is adjustable by at least one of thethrottle 16, theintake VVT 23, theexhaust VVT 26 and thewastegate valve 54. - In the present embodiment, the pumping loss is adjusted such that an integrated amount (that is, a total amount) of gas that is emitted from the
internal combustion engine 1 in a period from when supply of fuel to theinternal combustion engine 1 is stopped to when the rotation speed of theinternal combustion engine 1 becomes zero becomes the amount of gas, which corresponds to the volume of theexhaust passage 7 from an outlet of the cylinder 2 (that is, the boundary between thecylinder 2 and the exhaust port 71) to an inlet of theSCR catalyst 33. Because no fuel is supplied to theinternal combustion engine 1, the integrated amount of gas that is emitted from theinternal combustion engine 1 is equal to an integrated intake air amount of theinternal combustion engine 1. In the present embodiment, the amount of gas, which corresponds to the volume of theexhaust passage 7 from the outlet of thecylinder 2 to the inlet of theSCR catalyst 33, corresponds to a predetermined air amount in the meaning of the disclosure. The pumping loss when the opening degree of thethrottle 16 is small is larger than the pumping loss when the opening degree of thethrottle 16 is large. The pumping loss when the opening degree of thewastegate valve 54 is small is larger than the pumping loss when the opening degree of thewastegate valve 54 is large. For example, the pumping loss increases as the timing at which the opening degree of each of theintake valve 5 and theexhaust valve 9 becomes largest is more shifted from the timing at which the speed of thepiston 15 is highest. - A time from when supply of fuel to the
internal combustion engine 1 is stopped to when the rotation speed of theinternal combustion engine 1 becomes zero is influenced by not only the pumping loss but also a friction loss. Because the friction loss increases as the temperature of theinternal combustion engine 1 decreases, a time up to when the rotation speed of theinternal combustion engine 1 becomes zero shortens. In the present embodiment, a coolant temperature is detected as the temperature of theinternal combustion engine 1, and the pumping loss is adjusted in response to the coolant temperature. In the present embodiment, an example in which the pumping loss is adjusted on the basis of the predetermined air amount and the coolant temperature will be described. Instead, the pumping loss may be adjusted on the basis of only any one of the predetermined air amount and the coolant temperature. -
FIG. 9 is a graph that shows the relationship among a coolant temperature of theinternal combustion engine 1, an integrated intake air amount (predetermined air amount) that is required from when supply of fuel to theinternal combustion engine 1 is stopped to when the rotation speed of theinternal combustion engine 1 becomes zero, and a required pumping loss. The required pumping loss is such a pumping loss that an integrated amount of gas that is emitted from theinternal combustion engine 1 in a period from when supply of fuel to theinternal combustion engine 1 is stopped to when the rotation speed of theinternal combustion engine 1 becomes zero is equal to the amount of gas, which corresponds to the volume of theexhaust passage 7 from the outlet of thecylinder 2 to the inlet of theSCR catalyst 33. The predetermined air amount is a value corresponding to the volume of theexhaust passage 7 from the outlet of thecylinder 2 to the inlet of theSCR catalyst 33. This value may be obtained in advance. The coolant temperature may be obtained with the use of thecoolant temperature sensor 96. The amount of oxygen, which is required until the air-fuel ratio in theNSR catalyst 32 becomes the stoichiometric air-fuel ratio, varies depending on the oxygen storage capability of each of the three-way catalyst 31 and theNSR catalyst 32. Because the oxygen storage capability of each of the three-way catalyst 31 and theNSR catalyst 32 varies depending on degradation, or the like, the predetermined air amount may be changed in response to the oxygen storage capability of each of the three-way catalyst 31 and theNSR catalyst 32. However, in the present embodiment, for the purpose of providing simpler control, a change in the oxygen storage capability of each of the three-way catalyst 31 and theNSR catalyst 32 is not considered. - As shown in
FIG. 9 , as the predetermined air amount increases, the required pumping loss reduces. That is, as the predetermined air amount increases, it is required to operate theinternal combustion engine 1 for a longer time, so the required pumping loss reduces. As the coolant temperature decreases, the required pumping loss reduces. That is, as the coolant temperature decreases, the friction loss increases, so the required pumping loss may be smaller. - The relationship shown in
FIG. 9 may be obtained in advance by an experiment, simulation, or the like. The required pumping loss is obtained by the use of the relationship shown inFIG. 9 , and an actual pumping loss is adjusted to the required pumping loss. The relationship among a required pumping loss, an opening degree of thethrottle 16, an open/close timing of theintake valve 5, an open/close timing of theexhaust valve 9, and an opening degree of thewastegate valve 54 is obtained in advance by an experiment, simulation, or the like. A map for directly obtaining the opening degree of thethrottle 16, the open/close timing of theintake valve 5, the open/close timing of theexhaust valve 9 and the opening degree of thewastegate valve 54 from a predetermined air amount and a coolant temperature without obtaining a required pumping loss may be prepared and stored in theECU 90. -
FIG. 10 is a time chart that shows changes in various numeric values at the time of a stop of theinternal combustion engine 1. The continuous lines indicate the case where control according to the present embodiment is executed. The dashed lines indicate the case where control according to the third embodiment is executed. The continuous lines and the dashed lines take the same paths until T4.FIG. 11 is a time chart that shows changes in engine rotation speed, throttle opening degree and wastegate valve opening degree at the time of a stop of theinternal combustion engine 1. InFIG. 11 , in the throttle opening degree and the wastegate valve opening degree, the continuous lines indicate the case where the required pumping loss is small, and the alternate long and short dashes lines indicate that the required pumping loss is large. Like signs T1 to T6 inFIG. 10 andFIG. 11 denote the same times as those inFIG. 6 . - When the SCR output A/F becomes the stoichiometric air-fuel ratio at T4, supply of fuel to the
internal combustion engine 1 is stopped in the present embodiment. Thus, the rotation speed of theinternal combustion engine 1 decreases after T4; however, at least one of the opening degree of thethrottle 16, the open/close timing of theintake valve 5, the open/close timing of theexhaust valve 9 and the opening degree of thewastegate valve 54 is set in response to the required pumping loss. Thus, the degree of decrease in engine rotation speed is adjusted, so the amount of air that is emitted to theexhaust pipe 72 is also adjusted. The pumping loss may be adjusted at T4 or may be adjusted before T4 or after T4. For example, when the hydraulic pressure that is generated with the use of theinternal combustion engine 1 is required or the power of theinternal combustion engine 1 is required in order to adjust the pumping loss, the pumping loss may be adjusted while fuel is supplied to theinternal combustion engine 1. That is, even when the SCR output A/F becomes the stoichiometric air-fuel ratio, fuel for adjusting the pumping loss may be supplied. - At time T7 at which the rotation speed of the
internal combustion engine 1 becomes zero, the NSR output A/F is the stoichiometric air-fuel ratio. At T7, the three-way catalyst 31 is almost filled with air, and the three-way catalyst output A/F is higher than the stoichiometric air-fuel ratio. On the other hand, at T7, air has not reached theSCR catalyst 33, so the SCR output A/F is a rich air-fuel ratio. -
FIG. 12 is a flowchart of control at the time of a stop of theinternal combustion engine 1 according to the present embodiment. The flowchart is executed by theECU 90 at predetermined time intervals during operation of theinternal combustion engine 1. Like step numbers denote steps of the same processes as those of the steps of the above-described flowchart, and the description thereof is omitted. In the present embodiment, theECU 90 that processes the flowchart corresponds to an engine stop control unit in the meaning of the disclosure. - In the flowchart shown in
FIG. 12 , when affirmative determination is made instep S 103 or when negative determination is made in step S303, the process proceeds to step S401. In step S401, the required pumping loss is calculated. The required pumping loss is calculated on the basis ofFIG. 9 from the coolant temperature and predetermined air amount of theinternal combustion engine 1. In step S402, the pumping loss is adjusted such that the required pumping loss that is calculated in step S401 is equal to an actual pumping loss. After that, the process proceeds to step S104. As in the case of the first embodiment, at least one of step S201 and step S202 may be omitted. When step S202 is omitted, step S303 may also be omitted. - Incidentally, the friction loss can change depending on the individual difference, aged degradation, and the like, of each device. Thus, even when the required pumping loss is obtained in accordance with the relationship shown in
FIG. 9 , obtained in advance, the obtained required pumping loss may deviate from an actually required pumping loss. In the present embodiment, after the pumping loss is adjusted, the air-fuel ratio in each catalyst may be detected, and the required pumping loss may be corrected on the basis of the detected results. - For example, after the rotation speed of the
internal combustion engine 1 becomes zero, when the air-fuel ratio in theSCR catalyst 33 is a lean air-fuel ratio, air is emitted from theinternal combustion engine 1 more than necessary after supply of fuel to theinternal combustion engine 1 is stopped. In this case, it is possible to further early stop theinternal combustion engine 1 by correcting the required pumping loss such that the required pumping loss becomes larger, so it is possible to suppress a situation in which the air-fuel ratio in theSCR catalyst 33 becomes a lean air-fuel ratio. For example, the required pumping loss may be corrected by multiplying the required pumping loss by a predetermined coefficient or the required pumping loss may be corrected in response to an air-fuel ratio that is detected by the fourth air-fuel ratio sensor 94. - After the rotation speed of the
internal combustion engine 1 becomes zero, when the air-fuel ratio in the three-way catalyst 31 is lower than or equal to the stoichiometric air-fuel ratio, the amount of air emitted from theinternal combustion engine 1 after supply of fuel to theinternal combustion engine 1 is stopped is deficient. In this case, theinternal combustion engine 1 is allowed to be rotated longer by correcting the required pumping loss such that the required pumping loss becomes smaller, so it is possible to bring the air-fuel ratio in the three-way catalyst 31 to a lean air-fuel ratio. For example, the required pumping loss may be corrected by multiplying the required pumping loss by a predetermined coefficient or the required pumping loss may be corrected in response to an air-fuel ratio that is detected by the second air-fuel ratio sensor 92. - In addition, after the rotation speed of the
internal combustion engine 1 becomes zero, when the air-fuel ratio in theNSR catalyst 32 is a lean air-fuel ratio, the amount of air emitted from theinternal combustion engine 1 after supply of fuel to theinternal combustion engine 1 is stopped is deficient. In this case, theinternal combustion engine 1 is allowed to be rotated longer by correcting the required pumping loss such that the required pumping loss becomes smaller, so it is possible to bring the air-fuel ratio in theNSR catalyst 32 to the stoichiometric air-fuel ratio or higher. For example, the required pumping loss may be corrected by multiplying the required pumping loss by a predetermined coefficient or the required pumping loss may be corrected in response to an air-fuel ratio that is detected by the third air-fuel ratio sensor 93. -
FIG. 13 is a flowchart for correcting a required pumping loss. The flowchart is started when the rotation speed of theinternal combustion engine 1 becomes zero. - In step S501, it is determined whether the SCR output A/F is lower than or equal to the stoichiometric air-fuel ratio. In this step, it is determined whether the air-fuel ratio in the
SCR catalyst 33 is an appropriate value through stop control. When affirmative determination is made in step S501, the process proceeds to step S502. On the other hand, when negative determination is made in step S501, the process proceeds to step S506, and the pumping loss is increased. - In step S502, it is determined whether the three-way catalyst output A/F is higher than the stoichiometric air-fuel ratio. In this step, it is determined whether the air-fuel ratio in the three-
way catalyst 31 is an appropriate value through stop control. When affirmative determination is made in step S502, the process proceeds to step S503. On the other hand, when negative determination is made in step S502, the process proceeds to step S505, and the pumping loss is reduced. - In step S503, it is determined whether the NSR output A/F is higher than or equal to the stoichiometric air-fuel ratio. In this step, it is determined whether the air-fuel ratio in the
NSR catalyst 32 is an appropriate value through stop control. When affirmative determination is made in step S503, the process proceeds to step S504. On the other hand, when negative determination is made in step S503, the process proceeds to step S505, and the pumping loss is reduced. - In step S504, it is presumable that the required pumping loss is an appropriate value, so the flowchart is ended without correcting the required pumping loss.
- As described above, according to the present embodiment, it is not required to supply fuel to the
internal combustion engine 1 for the purpose of suppressing hydrocarbon poisoning in the three-way catalyst 31 and theNSR catalyst 32, so it is possible to reduce the consumption of fuel.
Claims (11)
- An exhaust gas control system for an internal combustion engine operable at a lean air-fuel ratio, the exhaust gas control system comprising:an NOx selective catalytic reduction catalyst (33) configured to be provided in an exhaust passage (72) of the internal combustion engine (1), the NOx selective catalytic reduction catalyst (33) being configured to adsorb ammonia and reduce NOx with the use of the adsorbed ammonia as a reducing agent; andan electronic control unit (90) configured to- change an air-fuel ratio in the internal combustion engine (1),- after a request to stop the internal combustion engine (1) has been issued, until an air-fuel ratio in the NOx selective catalytic reduction catalyst (33) becomes lower than or equal to a stoichiometric air-fuel ratio, operate the internal combustion engine (1) at the stoichiometric air-fuel ratio or lower, and- after that, execute a stop control that is a control for stopping supply of fuel to the internal combustion engine (1).
- The exhaust gas control system according to claim 1, further comprising:an upstream catalyst (31, 32) configured to be provided in the exhaust passage (72) at a portion upstream of the NOx selective catalytic reduction catalyst (33), the upstream catalyst (31, 32) being a catalyst of which exhaust gas purification performance decreases because of hydrocarbon poisoning, whereinthe electronic control unit (90) is configured to- in the stop control, until the air-fuel ratio in the NOx selective catalytic reduction catalyst (33) becomes lower than or equal to the stoichiometric air-fuel ratio, operate the internal combustion engine (1) at the stoichiometric air-fuel ratio or lower,- after that, until an air-fuel ratio in the upstream catalyst (31, 32) becomes higher than or equal to the stoichiometric air-fuel ratio while the air-fuel ratio in the NOx selective catalytic reduction catalyst (33) remains at the stoichiometric air-fuel ratio or lower, operate the internal combustion engine (1) at the stoichiometric air-fuel ratio or higher, and- after that, stop supply of fuel to the internal combustion engine (1).
- The exhaust gas control system according to claim 1, further comprising:an upstream catalyst (31, 32) configured to be provided in the exhaust passage (72) at a portion upstream of the NOx selective catalytic reduction catalyst (33), the upstream catalyst (31, 32) being a catalyst of which exhaust gas purification performance decreases because of hydrocarbon poisoning, whereinthe electronic control unit (90) is configured to adjust a pumping loss of the internal combustion engine (1) such that, in the stop control, a total intake air amount of the internal combustion engine (1) in a period from when supply of fuel to the internal combustion engine (1) is stopped to when a rotation speed of the internal combustion engine (1) becomes zero becomes a predetermined air amount, the predetermined air amount being a total intake air amount that is required to bring an air-fuel ratio in the upstream catalyst (31, 32) to the stoichiometric air-fuel ratio or higher while the air-fuel ratio in the NOx selective catalytic reduction catalyst (33) remains lower than or equal to the stoichiometric air-fuel ratio.
- The exhaust gas control system according to claim 3, wherein
the electronic control unit (90) is configured to set the pumping loss such that the pumping loss when the predetermined air amount is small is larger than the pumping loss when the predetermined air amount is large. - The exhaust gas control system according to claim 3 or 4, wherein
the electronic control unit (90) is configured to set the pumping loss such that the pumping loss when a temperature of the internal combustion engine (1) is high is larger than the pumping loss when the temperature of the internal combustion engine (1) is low. - The exhaust gas control system according to any one of claims 2 to 5, wherein
the upstream catalyst includes at least one of a three-way catalyst (31) and an NOx storage reduction catalyst (32),
the three-way catalyst (31) is a catalyst that is configured to be provided in the exhaust passage (72) of the internal combustion engine (1) and that has an oxygen storage capability, and
the NOx storage reduction catalyst (32) is a catalyst that is configured to be provided in the exhaust passage (72) at a portion downstream of the three-way catalyst (31), that stores NOx when the air-fuel ratio in the NOx storage reduction catalyst (32) is a lean air-fuel ratio, and that reduces NOx when the air-fuel ratio in the NOx storage reduction catalyst (32) is lower than or equal to the stoichiometric air-fuel ratio. - The exhaust gas control system according to claim 1, wherein
the electronic control unit (90) is configured to, when a request to stop the internal combustion engine (1) has been issued and when a condition for self-consumption of ammonia adsorbed in the NOx selective catalytic reduction catalyst (33) is satisfied, execute the stop control. - The exhaust gas control system according to claim 7, further comprising:an air-fuel ratio detection unit (94) configured to detect or estimate the air-fuel ratio in the NOx selective catalytic reduction catalyst (33), whereinthe electronic control unit (90) is configured to, when the air-fuel ratio detected or estimated by the air-fuel ratio detection unit (94) is a lean air-fuel ratio, determine that the condition for self-consumption of ammonia adsorbed in the NOx selective catalytic reduction catalyst (33) is satisfied.
- The exhaust gas control system according to claim 7 or 8, further comprising:a temperature detection unit (99) configured to detect or estimate a temperature in the NOx selective catalytic reduction catalyst (33), whereinthe electronic control unit (90) is configured to, when the temperature detected or estimated by the temperature detection unit (99) is higher than or equal to a lower limit temperature, determine that the condition for self-consumption of ammonia adsorbed in the NOx selective catalytic reduction catalyst (33) is satisfied, andthe lower limit temperature is a temperature at which self-consumption of ammonia adsorbed in the NOx selective catalytic reduction catalyst (33) begins.
- The exhaust gas control system according to any one of claims 7 to 9, further comprising:a temperature detection unit (99) configured to detect or estimate a temperature in the NOx selective catalytic reduction catalyst (33),the electronic control unit (90) is configured to, when the temperature detected or estimated by the temperature detection unit (99) is lower than an upper limit temperature, determine that the condition for self-consumption of ammonia adsorbed in the NOx selective catalytic reduction catalyst (33) is satisfied, andthe upper limit temperature is an upper limit value of a temperature at which ammonia remains in the NOx selective catalytic reduction catalyst (33).
- An exhaust gas control method for an internal combustion engine operable at a lean air-fuel ratio and comprising an NOx selective catalytic reduction catalyst (33) provided in an exhaust passage (72) of the internal combustion engine (1), the NOx selective catalytic reduction catalyst (33) being configured to adsorb ammonia and reduce NOx with the use of the adsorbed ammonia as a reducing agent,
the exhaust gas control method comprising the following steps:- changing an air-fuel ratio in the internal combustion engine (1),- after a request to stop the internal combustion engine (1) has been issued, until an air-fuel ratio in the NOx selective catalytic reduction catalyst (33) becomes lower than or equal to a stoichiometric air-fuel ratio, operating the internal combustion engine (1) at the stoichiometric air-fuel ratio or lower, and- after that, executing a stop control that is a control for stopping supply of fuel to the internal combustion engine (1).
Applications Claiming Priority (1)
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JP2015042904A JP6252518B2 (en) | 2015-03-04 | 2015-03-04 | Exhaust gas purification device for internal combustion engine |
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EP3064729A1 true EP3064729A1 (en) | 2016-09-07 |
EP3064729B1 EP3064729B1 (en) | 2017-10-11 |
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EP16158348.9A Not-in-force EP3064729B1 (en) | 2015-03-04 | 2016-03-03 | Exhaust gas control system for internal combustion engine |
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US (1) | US10202920B2 (en) |
EP (1) | EP3064729B1 (en) |
JP (1) | JP6252518B2 (en) |
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Cited By (1)
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---|---|---|---|---|
EP3533979A1 (en) * | 2018-03-02 | 2019-09-04 | Toyota Jidosha Kabushiki Kaisha | Exhaust gas purification apparatus for internal combustion engine |
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JP6213523B2 (en) * | 2015-06-09 | 2017-10-18 | トヨタ自動車株式会社 | Control device for internal combustion engine |
JP6586944B2 (en) * | 2016-12-27 | 2019-10-09 | トヨタ自動車株式会社 | Exhaust gas purification device for internal combustion engine |
US10337374B2 (en) * | 2017-03-15 | 2019-07-02 | Ford Global Technologies, Llc | Methods and systems for an aftertreatment catalyst |
JP6614187B2 (en) * | 2017-03-22 | 2019-12-04 | トヨタ自動車株式会社 | Exhaust gas purification device for internal combustion engine |
JP6617750B2 (en) * | 2017-05-23 | 2019-12-11 | トヨタ自動車株式会社 | Control device for vehicle drive device |
JP7077883B2 (en) * | 2018-09-06 | 2022-05-31 | トヨタ自動車株式会社 | Exhaust purification device for internal combustion engine |
CN110761882B (en) * | 2019-12-26 | 2020-04-07 | 潍柴动力股份有限公司 | Method and system for judging SCR sulfur poisoning |
US11300064B2 (en) * | 2020-07-01 | 2022-04-12 | Ford Global Technologies, Llc | Methods and systems for an aftertreatment system |
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2016
- 2016-03-02 US US15/058,428 patent/US10202920B2/en active Active
- 2016-03-03 EP EP16158348.9A patent/EP3064729B1/en not_active Not-in-force
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JP2016160900A (en) | 2016-09-05 |
CN105937424B (en) | 2019-02-15 |
US10202920B2 (en) | 2019-02-12 |
EP3064729B1 (en) | 2017-10-11 |
CN105937424A (en) | 2016-09-14 |
US20160258373A1 (en) | 2016-09-08 |
JP6252518B2 (en) | 2017-12-27 |
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